Pt/(100) β-Ga2O3 Schottky barrier diodes were fabricated using a plate cleaved from the crystal grown by Czochralski method. Their electroconductive and photoelectric characteristics were studied. The following values were obtained: the Schottky barrier height (1.69/1.62/1.74 eV), ideality coefficient (1.09/1.14), saturation current density (9.91 × 10–15 A/cm2), diode series resistance (7.98 kΩ), and net donor concentration [(1.8–2.4) × 1018 cm–3]. The diodes demonstrate a high rectification ratio of 1010 at an applied voltage of ± 1 V and a relatively low experimental value of the leakage current density ∼10–11 A/cm2. These structures are solar-blind and also capable of operating in self-powered mode. The diodes are highly sensitive to short-wave ultraviolet radiation with a wavelength λ ≤ 265 nm. The maximum values of responsivity (20.4 A/W), external quantum efficiency (1.2 × 104%), and detectivity (9.6 × 1015 Hz0.5 × cm × W–1) of diodes were registered under exposure to irradiation at λ = 210 nm and at applied voltage of −1 V. The responsivity and external quantum efficiency values in the self-powered operation mode were 12.3 A/W and 7.2 × 103%, respectively. The diodes showed low rise and decay times in self-powered operation mode for photodiode based on Ga2O3: 14 and 30 ms, respectively.

Monoclinic gallium oxide is characterized by a large bandgap energy Eg ∼ 4.5–4.9 eV, high electric breakdown field Ebr ⁓ 8 MV/cm, and high theoretical Baliga’s figure of merit (BFOM), which is 3444,1–5 versus 340 and 870 for SiC and GaN, respectively. β-Ga2O3 is rapidly gaining popularity as a base material for power electronics elements, which are promising for improving electrical energy conversion systems for electric vehicles, air conditioning, and power distribution systems.6–9 Furthermore, this ultrawide bandgap (UWBG) semiconductor is being considered for the development of solar-blind ultraviolet (UV) detectors and gas sensors.10–14 β-Ga2O3 bulk crystals are grown utilizing melt growth techniques such as the Czochralski process (CZ), edge-defined film-fed growth (EFG), and floating zone method (FZ).15,16 Such substrates possess relatively low dislocation density ⁓103 cm–2 and high crystal perfection.1,2,17 High quality commercial β-Ga2O3 wafers with a diameter of 4 in. are now available, which allows to create semiconductor devices based on them. In addition, methods are being developed to create functional regions of power diodes and transistors based on β-Ga2O3 substrates by doping in the process of epitaxy, diffusion, and ion implantation.18–20 It was shown that β-Ga2O3 can be doped with a shallow donor with a concentration of ∼1021 cm–3.1 By now, Schottky barrier diodes (SBDs) based on β-Ga2O3 with a breakdown voltage Ubr of up to 10 kV, capable of operating at high electric fields of 6.94 MV/cm, and heterojunctions diodes with Ubr = 13.5 kV are being successfully developed.21–27 Vertical and planar metal–oxide–semiconductor field effect transistors (MOSFETs) with Ubr up to 8–10 kV, cutoff frequency 48 GHz, Ebr = 5.4 MV/cm, and turn-on resistance ∼3–18 mΩ × cm2 were obtained.6,28–32 The high Eg and the possibility to obtain high quality films and wafers make β-Ga2O3 a promising material for the development of solar-blind UV detectors with an operating wavelength range of 200–280 nm without the use of spectral filters.33,34 Low power consumption and the ability to operate autonomously (self-powered mode) are important requirements for detectors, which p-n junction diodes, heterostructures, photoelectrochemical photodetectors, and SBDs meet.35 SBDs, in particular, have a number of advantages: high-speed performance, low dark currents, and relative ease of fabrication.36 

Structures based on (100) β-Ga2O3 crystals still remain poorly studied; hence, there are rare examples of device development. The SBDs utilizing EFG grown (100) β-Ga2O3 substrates were studied in Ref. 37. These diodes demonstrate attractive electrical characteristics: high rectification ratio of 1010, ideality factor of 1.1, high Schottky barrier height of 1.3–1.39 eV, high forward current density of 50–150 A/cm2 at applied voltage of 2 V, and low saturation current density of 2 × 10–16 A/cm2.

In this work, we developed an SBD based on the Pt/(100) β-Ga2O3 interface and studied its electroconductive and photoelectric properties. The substrate crystal was grown by the CZ method.

A bulk crystal of beta-gallia in the form of a cylindrical boule was grown by CZ. The growth was carried out using a modified Nika crystal puller produced by EZAN. This device utilizes an induction heater and zirconia thermal insulation. The process was performed in iridium crucible, gallium oxide powder (99.99% purity) was used as a raw material, and gallium oxide crystal was used as a seed. A 2% oxygen/argon atmosphere was maintained during growth. The growth rate was kept at 2 mm/h. The process parameters are described in detail in Refs. 17 and 38. Then, the crystal was cleaved into fragments presumably along the cleavage planes. Such unintentionally doped (UID) Ga2O3 substrates have ∼600 μm thickness. These samples were considered for the investigation and further were used as the base material for the fabrication of vertical type SBD samples.

Phase composition and crystal perfection of these samples were studied by the x-ray diffraction (XRD) technique. A set of XRD patterns were measured in the vicinities of β-Ga2O3 400, 600, 800, and 12 000 reflections in the θ–2θ mode, and β-Ga2O3 200 and 400 ω-scanning curves were registered. The data were collected with the help of a modified Bourevestnik DRON-7 lab device with an enhanced base, in the quasiparallel mode, using an SCSD-4C scintillation detector and a Ge (111) monochromator crystal, with the Cu Kα1 radiation (1.540562 Å) applied. All the sequences of XRD curves were treated via the Williamson–Hall method typically performed at a set of XRD reflections corresponding to the same sample lattice direction.39 The technique is based on the fact that the full width at half maximum (FWHM) values of XRD reflection curves (denoted here as W) are formed by two dominating factors, namely, crystallite sizes and microstresses. If one assumes XRD peaks to be fitted by convoluted Gauss functions, then the W value can be presented as follows:
W 2 = ( λ b / t z ) 2 + [ ( 4 ε ) 2 + ( λ b / t z ) 2 ] × ta n 2 θ b ,
(1)
where λb denotes the beam wavelength; ε is the root mean square (RMS) of the microstrain along the wavevector direction; tz corresponds to the coherent-domain-size (CDS) in the same direction;40 and θb means the Bragg scattering angle. The W2(tan2θb) dependence appears, thus, to be linear. Therefore, FWHM magnitudes of XRD reflections vs. Bragg scattering angles can yield two sample structure parameters, namely, ε and tz.

For sample surface visualization, a Nikon Eclipse E200 high resolution optical microscope was applied. For higher magnification, we used an SEC SNE-4500 Plus scanning electron microscope (SEM) with the accelerating voltage of 10 kV. The surface relief was scanned by an MNT AFM-1000 atomic force microscope (AFM) operating in the tapping mode. Separate scans of the surface relief for the calculation of the roughness values were registered by a Mahr MarSurf PS10 profilometer.

Transmission spectra of (100) β-Ga2O3 plates were measured using a combined DH-2000 radiation source based on deuterium and tungsten halogen lamps and an Ocean Optics spectrometric system at room temperature. The wavelength λ was measured with an optical resolution of ∼1 nm.

The β-Ga2O3 plate was treated with acetone, isopropyl alcohol, and de-ionized water prior to the deposition of the Pt anode and Ti ohmic contact. A 1 mm diameter, 100 nm thick Pt anode was deposited on the β-Ga2O3 plate surface by DC magnetron sputtering through a shadow mask. A continuous 100 nm thick ohmic Ti contact was deposited by DC magnetron sputtering on the back of the β-Ga2O3 wafer. During contact deposition, the β-Ga2O3 plate was heated up to 200 °С to improve metals’ adhesion.

Measurements of the electroconductive characteristics of the SBD were carried out under dark conditions in a sealed Nextron MPS-CHH chamber equipped with microprobes. The samples were placed on a ceramic table, which heats up to a temperature of T = 750 °С with an accuracy of ± 0.1 °С. The atmosphere in the chamber consisted of pure and dry air. I-U (J-U) and C-U characteristics were measured using a Keithley 2636A source-meter and E4980A RLC meter, respectively, where I is the current through the sample, U is the applied voltage, J is the current density, and C is the electrical capacitance.

The spectral dependences of the SBD photoelectric characteristics were measured using a MonoScan 2000 monochromator (Ocean Optics). A DH-2000 lamp was used as the source of optical radiation. The transmitted radiation was analyzed by means of the Ocean Optics Flame spectrometer with an operating range of Δλ = 200–850 nm. The measurements were controlled using OceanView software. A krypton-fluorine lamp VL-6.C was used as the source of irradiation at λ = 254 nm and the light power density of 620 μW/cm2. The measurements were carried out in an automated mode at room temperature and humidity. The speed-performance of the SBD was studied using a UV light emitting diode with maximum radiation intensity at λ = 250 nm, controlled by a high-speed transistor.

The sample cleaved surface contains multiple rectangular terraces with sizes of approximately (100 × 25) μm elongated toward a common direction [see Fig. 1(a)].38 Surface fragments belonging to a single terrace do not manifest distinguishable inhomogeneities at microscale [see Fig. 1(b)]. The heights of the terraces vary in the range from 100 to 200 nm, and the terraces have a typical size of 150 nm [see a steplike relief feature in Fig. 1(c)]. The cleaved surface possesses a relatively high roughness with the average value Ra = 84 nm measured at five samples in both perpendicular directions.

FIG. 1.

Optical image of the Ga2O3 bulk crystal; cleaved surface displays the aligned terraces (a). SEM image of the surface within a single terrace (b), AFM image of the zoomed part of a single terrace (c).

FIG. 1.

Optical image of the Ga2O3 bulk crystal; cleaved surface displays the aligned terraces (a). SEM image of the surface within a single terrace (b), AFM image of the zoomed part of a single terrace (c).

Close modal

No reflections were detected in the θ–2θ XRD mode except for monoclinic Ga2O3 h00 ones, which confirms that the samples are single-crystalline. Figure 2(a) represents the registered θ–2θ curve corresponding to the β-Ga2O3 400 reflection for one of the studied samples. Figure 2(b) shows the ω-scanning curve (FWHM = 30 arcsec) for the β-Ga2O3 400 reflection obtained at the same sample. The registered angular positions of 400, 600, 800, and 1200 θ–2θ XRD reflections appeared to be about 30.05°, 45.84°, 62.52°, and 102.20°, respectively. These data are in good agreement with reference magnitudes presented in the ICDD card 00-041-1103, which are 30.08°, 45.82°, 62.53°, and 102.25° for the corresponding reflections listed above, respectively.

FIG. 2.

β-Ga2O3 400 XRD curve measured in the θ–2θ mode at the (100) sample surface (a); the β-Ga2O3 200 ω-scanning XRD curve at the same sample surface (b).

FIG. 2.

β-Ga2O3 400 XRD curve measured in the θ–2θ mode at the (100) sample surface (a); the β-Ga2O3 200 ω-scanning XRD curve at the same sample surface (b).

Close modal

The Williamson–Hall method was applied to the described set of β-Ga2O3 400, 600, 800, and 1200 θ–2θ XRD pattern fragments. The calculated (toward [100] direction) CDS value happened to be about 900 nm, while the microstrain appeared to be close to 1.1 × 10–4. Figure 3 represents the Williamson–Hall plot with linear fitting (the blue line) for squared FWHM reflection peaks value dependence on tan2(θ). The extremely low fitting discrepancy indicates that both the microstrain and CDS estimations are adequate.

FIG. 3.

Williamson–Hall plot for the θ–2θ pattern fragments for h00 reflections. The dots represent the experimental FWHM reflection peak values. The solid line is a linear fit.

FIG. 3.

Williamson–Hall plot for the θ–2θ pattern fragments for h00 reflections. The dots represent the experimental FWHM reflection peak values. The solid line is a linear fit.

Close modal

Figure 4(a) shows the spectral dependence for the transmittance of β-Ga2O3 plates (the black plot). The samples exhibit high transmittance values, corresponding to 60%–80% in the range of λ = 280–410 nm. The optical bandgap of the β-Ga2O3 was calculated by means of the Tauc plot [Fig. 4(b)] with estimated Eg = 4.67 eV. The analysis of the Tauc plot followed the methods described in Ref. 41. In Fig. 4(b), α is the absorption coefficient and hν is the energy of the incident photon. The measured absorption spectra contain an energy band where the energy of the optical transitions exceeds the energy of half the band gap.

FIG. 4.

Transmission spectrum of the Czochralski grown (100) β-Ga2O3 plate (a); the Tauc plot of the Czochralski grown (100) β-Ga2O3 plate (b).

FIG. 4.

Transmission spectrum of the Czochralski grown (100) β-Ga2O3 plate (a); the Tauc plot of the Czochralski grown (100) β-Ga2O3 plate (b).

Close modal
We can assume the contribution of trap states (which were previously discovered for these crystals in study7) in the recorded spectrum. In this case, absorption is described by the following expression:42,
α ( h ν ) = B 1 ( h ν ) 3 ( h ν E t ) 0.5 + B 2 ( h ν E g ) 0.5 ,
(2)
where B1 and B2 are the constants and Et is the energy gap associated with the trap state. The transmittance experimental spectrum in the absorption edge region closely matches the result obtained from the approximation of expression (2) at Eg = 4.6 eV and Et = 4.4 eV [shown as the red curve in Fig. 4(a)]. This occurrence will be considered separately in further research. On the other hand, a similar structure of the transmission spectra has previously been observed for (100) β-Ga2O3 and was connected to the anisotropy of crystal optical properties during the transmission of unpolarized or polarized radiation.9,43

Figure 5 shows the forward J-U characteristic of the SBD based on Pt/β-Ga2O3. The current density values increase from 1.73 pA/cm2 to 248 mA/cm2 as the applied voltage increases from 0.01 to 1 V. The ON-resistance Ron and ON-voltage Uon of the SBD are 683.7 mΩ × cm2 and 0.82 V, respectively. These values were determined from the analysis of the linear section of the forward J-U characteristic. The leakage current is ∼1 × 10–13 A.

FIG. 5.

Forward branch of J-U characteristic of the SBD based on Pt/β-Ga2O3. Inset shows the J-U characteristics in a semilogarithmic scale.

FIG. 5.

Forward branch of J-U characteristic of the SBD based on Pt/β-Ga2O3. Inset shows the J-U characteristics in a semilogarithmic scale.

Close modal
According to the thermionic emission (TE) model, the J-U characteristic of a Schottky barrier diode can be approximated by the following expression:1,34
J = J s [ exp ( e U / ( n k T k ) ) 1 ] ,
(3)
where Js is the saturation current density, e is the electron charge, n is the ideality coefficient, k is the Boltzmann constant, and Tk is the absolute temperature of the sample. Expression (3) can be rewritten as follows at U ≥ 0.3 V:
ln ( J / J s ) = e U / ( n k T k ) .
(4)
In this case, the ideality coefficient can be calculated from the slope of the linear dependence ln(J/Js) vs U. The n value is 1.09 for the considered SBDs based on the Pt/β-Ga2O3. The Js value is 9.91 × 10–15 A/cm2 calculated from extrapolation of the linear section of the forward J-U characteristic to 0 V. According to the TE model, Js can be expressed as follows:1,34
J s = S eff A T k 2 × exp [ e Φ b / ( n k T k ) ] ,
(5)
where Seff is the effective anode area, A* = 3.35 × 105 A/(cm–2 × K–2) is the Richardson constant, and Фb is the height of the Schottky barrier. Expression (5) was used to determine Фb,
Φ b = ln ( A T k 2 S eff / J s ) × n k T k / e .
(6)

The Фb value at the Pt/β-Ga2O3 interface is 1.69 eV according to the TE model and the analysis of the J-U characteristics.

In addition, the J-U characteristics of SBD based on the Pt/β-Ga2O3 were analyzed using Cheng’s method.1,44 The following expression can be used for an SBD:
U = J R s S eff + n Φ b + ( n k T k / e ) × ln [ J / ( A T k 2 ) ] ,
(7)
H ( J ) = U ( n k T k / e ) × ln [ J / ( A T k 2 ) ] ,
(8)
where Rs is the series resistance of SBD and H is the defined function. Expression(7) after differentiation with respect to J can be written as follows:
d U / d ln ( J ) = J R s S eff + n k T / e .
(9)
From the analysis of the dependence of dU/dln(J) on J (Fig. 6), Rs and n were determined, which were 7.98 kΩ and 1.14, respectively. From expressions (7) and (8), it follows that
H ( J ) = R s S eff J + n Φ b .
(10)
FIG. 6.

Cheng’s method plots of dU/dln(J) vs J and H(J) vs J for the SBD based on Pt/β-Ga2O3.

FIG. 6.

Cheng’s method plots of dU/dln(J) vs J and H(J) vs J for the SBD based on Pt/β-Ga2O3.

Close modal

The Фb = 1.62 eV was determined by analyzing the dependence H(J) using the previously obtained Rs and n (Fig. 6). The ideality coefficient and the height of the Schottky barrier obtained by means of the TE model and Cheng’s method exhibit slight differences.

The C-U characteristics of the SBD based on Pt/β-Ga2O3 were measured using a signal with a voltage amplitude of 100 mV and frequencies of 1, 2, 5, and 10 kHz (Fig. 7). The net donor concentration Nd and Фb value were determined from the analysis of the Seff2/C2 vs U curves using the following expressions, respectively:1,34
N d = 2 / ( e ε r ε 0 b ) ,
(11)
Φ b = e N d ε r ε 0 A / 2 ,
(12)
where ɛr = 10 is the dielectric constant for β-Ga2O3,1, ɛ0 is the dielectric constant, b is the slope of the linear section of the C-U characteristic in coordinates of Seff2/C2 vs U, and A is the intersection of the Seff2/C2 curve with the x-axis (Fig. 7). The calculated values of Nd and Фb were (1.8–2.4) × 1018 cm–3 and 1.74 eV, respectively. The contact potential difference eUc of 1.69 eV determined from the analysis of the C-U characteristics. The relatively high Nd value is a consequence of the specific characteristics of the β-Ga2O3 crystal growth method and is contingent upon a multitude of variables, including the impact of the crucible material and the purity of the starting material.15 During the growth of β-Ga2O3 crystals, conditions are created that facilitate the formation of donor-type defects, resulting in an increase in Nd.
FIG. 7.

C-U characteristics of the SBD based on Pt/β-Ga2O3. Inset shows the dependence of Seff2/C2 vs U.

FIG. 7.

C-U characteristics of the SBD based on Pt/β-Ga2O3. Inset shows the dependence of Seff2/C2 vs U.

Close modal

One of the defining characteristics of power diodes is Ubr. In this study, we did not employ any special techniques to achieve high Ubr values. Given the relatively simple SBD manufacturing technology, Ubr corresponded to 50 V.

Table I compares the electroconductive characteristics of SBDs based on β-Ga2O3. The studied SBDs exhibit a high rectification coefficient of 1010 and a low Uon of 0.82 V. The high ON-resistance is attributed to the structure’s high resistance at low bias.

TABLE I.

Electroconductive characteristics of SBDs based on β-Ga2O3.

AnodeRon (mΩ × cm2)nФb (eV)Uon (V)Rectification ratioJs (A/cm2)Reference
Au/Pt 1.83 1.05 1.24 0.9 109 5 × 10–15 33  
Ti/SnOx 60 1.02 1.19 — >1010 — 45  
Au/Ni 190 Ω × mm — — 0.85–0.9 107–108 — 46  
Au/Ti/Pt 7.85 1.06 1.52 — — 6 × 10–19 47  
Au/W 10.5 1.02 1.07 — >106 — 48  
Au/Ni 1.08 1.1 — — — 49  
Ti/Pt 5.1 1.03 1.46 — — — 50  
Au/Ti/Pt 1.02 — <1010 — 51  
Pt 12.5 1.1 1.38 1.07  2 × 10–16 37  
Pt 683.7 1.09 1.69 0.82 1010 9.91 × 10–15 This work 
AnodeRon (mΩ × cm2)nФb (eV)Uon (V)Rectification ratioJs (A/cm2)Reference
Au/Pt 1.83 1.05 1.24 0.9 109 5 × 10–15 33  
Ti/SnOx 60 1.02 1.19 — >1010 — 45  
Au/Ni 190 Ω × mm — — 0.85–0.9 107–108 — 46  
Au/Ti/Pt 7.85 1.06 1.52 — — 6 × 10–19 47  
Au/W 10.5 1.02 1.07 — >106 — 48  
Au/Ni 1.08 1.1 — — — 49  
Ti/Pt 5.1 1.03 1.46 — — — 50  
Au/Ti/Pt 1.02 — <1010 — 51  
Pt 12.5 1.1 1.38 1.07  2 × 10–16 37  
Pt 683.7 1.09 1.69 0.82 1010 9.91 × 10–15 This work 
The photoelectric characteristics of SBDs were computed by means of the following formulas:13 
R = I ph / ( P × S ) ,
(13)
E Q E = [ R × h × c / ( e × λ ) ] × 100 % ,
(14)
D = R × S 1 / 2 / ( 2 × e × I D ) 1 / 2 ,
(15)
where R is the responsivity, Iph is the photocurrent, Iph = IL − ID, IL is the total current, ID is the dark current, S is the effective illumination area, P is the light power density, EQE is the external quantum efficiency, h is the Planck constant, c is the speed of light in vacuum, and D is the detectivity.

Figure 8 shows the I-U characteristics of the SBD based on Pt/β-Ga2O3. The diodes show an extremely low reverse dark current ID = (1–3) × 10–13 A for the ultraviolet photodiode in the range of U from −0.01 to −1 V. The ID value increases from 13 fA to 1.95 mA as U increases from 0.01 to 1 V. Exposure to radiation at λ = 254 nm and P = 620 μW/cm2 leads to a significant increase in the reverse current to 70–84 nA in the range of U from −0.01 to −1 V. The open-circuit voltage and short-circuit current of our SBD were 0.55 V and 70 nA, respectively.

FIG. 8.

I-U characteristics of the SBD under dark conditions and under exposure to irradiation at λ = 254 nm and P = 620 μW/cm2.

FIG. 8.

I-U characteristics of the SBD under dark conditions and under exposure to irradiation at λ = 254 nm and P = 620 μW/cm2.

Close modal

Figure 9 shows the spectral dependences of the photoelectric characteristics of the SBD in the range of λ = 210–360 nm and at U = –1 V. A noticeable increase in the photoelectric characteristics of the SBD is observed at λ = 265 nm. The R, EQE, and D increases sharply with a decrease in λ from 265 to 210 nm due to the band-to-band absorption of photons in β-Ga2O3 bulk. The maximum values of the photoelectric characteristics are observed at λ = 210 nm. The R, EQE, and D at λ = 210 nm were 20.4 A/W, 1.2 × 104%, and 9.6 × 1015 Hz0.5 × cm × W–1, respectively.

FIG. 9.

Spectral dependencies of responsivity (a), detectivity (b), and external quantum efficiency (c) of the SBD at U = –1 V.

FIG. 9.

Spectral dependencies of responsivity (a), detectivity (b), and external quantum efficiency (c) of the SBD at U = –1 V.

Close modal

SBDs based on Pt/β-Ga2O3 are able to function in the self-powered operation mode. Figure 10 shows the spectral dependencies of R and EQE at U = 0. The maximum values of R and EQE are 12.3 A/W and 7.2 × 103%, respectively, at λ = 210 nm. The photovoltaic effect observed in the studied SBDs can be attributed to the built-in electric field at the Pt/β-Ga2O3 interface.

FIG. 10.

Spectral dependencies of responsivity (a) and external quantum efficiency (b) of the SBD at U = 0.

FIG. 10.

Spectral dependencies of responsivity (a) and external quantum efficiency (b) of the SBD at U = 0.

Close modal
The rise and decay sections of the total current of the SBD in the self-powered mode (Fig. 11) and at U = –1 V under UV exposure are approximated with biexponential functions,
I L ( t ) = I Lst A 1 × exp [ t / τ r 1 ] A 2 × exp [ t / τ r 2 ] ,
(16)
I L ( t ) = I Dst + C 1 × exp [ t / τ d 1 ] + C 2 × exp [ t / τ d 2 ] ,
(17)
where ILst and IDst are the steady-state total and dark currents, respectively; t is the time; A1, A2, C1, and C2 are constants; τr1, τr2, τd1, and τd2 are the relaxation-time constants.52 It is important to note that τr1 ≫ τr2 and τd1 ≫ τd2. The fast-response components of τr1 and τd1 are typically a result of the rapid changes in the carrier concentration caused by the generation and recombination of carrier charges during light on/off cycles. The slow-response components of τr2 and τd2 are due to the carrier trapping/releasing from defects.53 The fast-response components largely determine the speed performance of the UV detectors, so the equations τr = τr1 and τd = τd1 are correct. The rise and decay times for SBDs based on Pt/β-Ga2O3 in the self-powered operation mode and under exposure to λ = 250 nm are 14 and 30 ms, respectively. τr and τd at U = –1 V are 17 and 27 ms, respectively. The high-speed performance of SBD is due to the presence of a built-in electric field at the metal/semiconductor interface.
FIG. 11.

Time dependencies of the normalized total currents through the SBD based on Pt/β-Ga2O3 at exposure to irradiation at λ = 250 nm, (a) U = 0 (self-powered mode) and (b) U = –1 V.

FIG. 11.

Time dependencies of the normalized total currents through the SBD based on Pt/β-Ga2O3 at exposure to irradiation at λ = 250 nm, (a) U = 0 (self-powered mode) and (b) U = –1 V.

Close modal

Table II compares the photoelectric characteristics of the SBDs based on Ga2O3. The considered here SBDs based on Czochralski grown (100) β-Ga2O3 exhibit both high-speed performance and are also capable of operating in the self-powered mode. Lower τr/ τd values in the self-powered mode were reported in Ref. 59 However, these results were also characterized by a low R.

TABLE II.

Photoelectric characteristics of SBDs based on Ga2O3.

MaterialResponsivity (A/W)τr/ τd (ms)Bias (V)Reference
β-Ga2O3 4 × 10–3 90/410 54  
a-Ga2O3 1021.8 144/208 –5 36  
β-Ga2O3 2.34 –/29.38 × 103 –10 55  
β-Ga2O3 0.6 320/270 –1.2 56  
β-Ga2O3 67 970/210 –5 57  
a-Ga2O3 0.23 × 10–6 240/– 58  
β-Ga2O3 3.7 × 10–2 9/9 59  
β-Ga2O3 12.3 14/30 This work 
MaterialResponsivity (A/W)τr/ τd (ms)Bias (V)Reference
β-Ga2O3 4 × 10–3 90/410 54  
a-Ga2O3 1021.8 144/208 –5 36  
β-Ga2O3 2.34 –/29.38 × 103 –10 55  
β-Ga2O3 0.6 320/270 –1.2 56  
β-Ga2O3 67 970/210 –5 57  
a-Ga2O3 0.23 × 10–6 240/– 58  
β-Ga2O3 3.7 × 10–2 9/9 59  
β-Ga2O3 12.3 14/30 This work 

Pt/(100) β-Ga2O3 Schottky barrier diodes were constructed on Czochralski grown crystal. These diodes are of interest for use as power rectifiers and high-speed autonomous solar-blind ultraviolet detectors. The current-voltage and capacitance-voltage characteristics of the diodes were analyzed at room temperature and dark conditions using the thermionic emission model and Cheng’s method. The calculated values of the Schottky barrier height, ideality coefficient, and saturation current density were 1.69 eV, 1.09, and 9.91 × 10–15 A/cm2, respectively, according to the thermionic emission model. According to Cheng’s method, the Schottky barrier height, ideality coefficient, and diode series resistance were 1.62 eV, 1.14, and 7.98 kΩ, respectively. The analysis of the capacitance-voltage characteristics of the diodes revealed that the height of the Schottky barrier was 1.74 eV and the value of the net donor concentration was (1.8–2.4) × 1018 cm–3. The diodes exhibited a high rectification ratio of 1010 at an applied voltage of ±1 V and a relatively low experimental value of the leakage current density of ∼10–11 A/cm2. Schottky barrier diodes were highly sensitive to irradiation at wavelengths below 265 nm, and their maximum sensitivity to UV radiation corresponds to a wavelength of 210 nm. The values of responsivity, external quantum efficiency, and detectivity of diodes were 20.4 A/W, 1.2 × 104%, and 9.6 × 1015 Hz0.5 × cm × W–1, respectively, at a wavelength of 210 nm and an applied voltage of −1 V. Schottky barrier diodes based on Pt/β-Ga2O3 are able to function in the self-powered operation mode. The responsivity and external quantum efficiency values were 12.3 A/W and 7.2 × 103%, respectively, at exposure to irradiation at 210 nm and in the self-powered operation mode. The diodes showed low rise and decay times in the self-powered operation mode for ultraviolet photodiodes based on Ga2O3: 14 and 30 ms, respectively.

Aleksei Almaev, Nikita Yakovlev, Alexander Tsymbalov, Viktor Kopyev, and Bogdan Kushnarev acknowledge the support the Decree of the Government of the Russian Federation No. 220 of April 9, 2010 (Agreement No. 075-15-2022-1132 of July 1, 2022). Aleksei Almaev and Nikita Yakovlev acknowledge the support from the Foundation for Promoting the Development of Small Forms of Enterprises in the Scientific and Technical Sphere under Project No. 4GUES18/91363.

The authors have no conflicts to disclose.

Aleksei Almaev: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Funding acquisition (equal); Project administration (equal); Supervision (equal); Writing – original draft (equal); Writing – review & editing (equal). Vladimir Nikolaev: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Funding acquisition (equal); Project administration (equal); Supervision (equal); Writing – original draft (equal); Writing – review & editing (equal). Nikita Yakovlev: Investigation (equal); Methodology (equal); Software (equal); Validation (equal); Visualization (equal); Writing – original draft (equal). Pavel Butenko: Formal analysis (equal); Investigation (equal); Methodology (equal); Resources (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Alexander Tsymbalov: Investigation (equal); Methodology (equal); Resources (equal); Software (equal); Visualization (equal); Writing – original draft (equal). Michael Boiko: Investigation (equal); Methodology (equal); Software (equal); Visualization (equal). Viktor Kopyev: Investigation (equal); Methodology (equal); Software (equal); Visualization (equal); Writing – original draft (equal). Vladimir Krymov: Investigation (equal); Methodology (equal); Resources (equal). Bogdan Kushnarev: Investigation (equal); Methodology (equal); Resources (equal). Sevastian Shapenkov: Investigation (equal); Methodology (equal); Software (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Michael Sharkov: Investigation (equal); Methodology (equal); Resources (equal). Anton Zarichny: Investigation (equal); Methodology (equal); Software (equal); Visualization (equal).

The data that support the findings of this study are available from the corresponding author upon reasonable request.

1.
H.
Sheoran
,
V.
Kumar
, and
R. A.
Singh
,
ACS Appl. Electron. Mater.
4
,
2589
(
2022
).
2.
B.
Fu
,
Z.
Jia
,
W.
Mu
,
Y.
Yin
,
J.
Zhang
, and
X.
Tao
,
J. Semicond.
40
,
011804
(
2019
).
3.
A. J.
Green
et al,
IEEE Electron Device Lett.
37
,
902
(
2016
).
4.
S. E.
Bennett
,
Mater. Sci. Technol.
26
,
1017
(
2010
).
5.
S.
Kitagawa
,
H.
Miyake
, and
K.
Hiramatsu
,
Jpn. J. Appl. Phys.
53
,
05FL03
(
2014
).
6.
K.
Zeng
,
A.
Vaidya
, and
U.
Singisetti
,
IEEE Electron Device Lett.
39
,
1385
(
2018
).
7.
M.
Orita
,
H.
Ohta
,
M.
Hirano
, and
H.
Hosono
,
Appl. Phys. Lett.
77
,
4166
(
2000
).
8.
H.
He
,
R.
Orlando
,
M. A.
Blanco
,
R.
Pandey
,
E.
Amzallag
,
I.
Baraille
, and
M.
Rerat
,
Phys. Rev. B
74
,
195123
(
2006
).
9.
T.
Onuma
,
S.
Saito
,
K.
Sasaki
,
T.
Masui
,
T.
Yamaguchi
,
T.
Honda
, and
M.
Higashiwaki
,
Jpn. J. Appl. Phys.
54
,
112601
(
2015
).
10.
X.
Sun
,
M.
Kong
,
O.
Alkhazragi
,
C.
Shen
,
E. N.
Ooi
,
X.
Zhang
,
U.
Buttner
,
T. K.
Ng
, and
B. S.
Ooi
,
Opt. Commun.
461
,
125264
(
2020
).
11.
12.
L.
Guo
,
Y.
Guo
,
J.
Wang
, and
T.
Wei
,
J. Semicond.
42
,
081801
(
2021
).
13.
A.
Almaev
et al,
IEEE Sens. J.
23
,
19245
(
2023
).
15.
Z.
Galazka
,
J. Appl. Phys.
131
,
031103
(
2022
).
16.
H. F.
Mohamed
,
C.
Xia
,
Q.
Sai
,
H.
Cui
,
M.
Pan
, and
H.
Qi
,
J. Semicond.
40
,
011801
(
2019
).
17.
V. I.
Nikolaev
et al,
ECS J. Solid State Sci. Technol.
13
,
015003
(
2024
).
18.
A. J.
Green
et al,
APL Mater.
10
,
029201
(
2022
).
20.
A.
Nikolskaya
et al,
J. Vac. Sci. Technol. A
39
,
030802
(
2021
).
21.
J.
Yang
,
F.
Ren
,
M.
Tadjer
,
S. J.
Pearton
, and
A.
Kuramata
,
ECS J. Solid State Sci. Technol.
7
,
Q92
(
2018
).
22.
M. J.
Tadjer
et al, “
Ga2o3 Schottky barrier and heterojunction diodes for power electronics applications
,” in
Gallium Nitride Materials and Devices XIII
(
SPIE
,
San Francisco
,
2018
), p.
1053212
.
23.
Z.
Hu
et al,
IEEE Electron Device Lett.
39
,
1564
(
2018
).
24.
X.
Huang
,
F.
Liao
,
L.
Li
,
X.
Liang
,
Q.
Liu
,
C.
Zhang
, and
X.
Hu
,
ECS J. Solid State Sci. Technol.
9
,
045012
(
2020
).
25.
Y.
Qin
et al,
IEEE Electron Device Lett.
44
,
1268
(
2023
).
26.
J. S.
Li
,
H. H.
Wan
,
C. C.
Chiang
,
T. J.
Yoo
,
M. H.
Yu
,
F.
Ren
,
H.
Kim
,
Y. T.
Liao
, and
S. J.
Pearton
,
ECS J. Solid State Sci. Technol.
13
,
035003
(
2024
).
27.
B.
Cromer
et al,
J. Vac. Sci. Technol. A
42
,
033206
(
2024
).
28.
Z.
Hu
,
K.
Nomoto
,
W.
Li
,
N.
Tanen
,
K.
Sasaki
,
A.
Kuramata
,
T.
Nakamura
,
D.
Jena
, and
H. G.
Xing
,
IEEE Electron Device Lett.
39
,
869
(
2018
).
29.
A. J.
Green
et al,
IEEE Electron Device Lett.
38
,
790
(
2017
).
30.
X.
Yan
,
I. S.
Esqueda
,
J.
Ma
,
J.
Tice
, and
H.
Wang
,
Appl. Phys. Lett.
112
,
032101
(
2018
).
31.
S.
Sharma
,
K.
Zeng
,
S.
Saha
, and
U.
Singisetti
,
IEEE Electron Device Lett.
41
,
836
(
2020
).
32.
C. N.
Saha
,
A.
Vaidya
,
A. F. M.
Anhar Uddin Bhuiyan
,
L.
Meng
,
S.
Sharma
,
H.
Zhao
, and
U.
Singisetti
,
Appl. Phys. Lett.
122
,
182106
(
2023
).
33.
C.
Xie
,
X.
Lu
,
Y.
Liang
,
H.
Chen
,
L.
Wang
,
C.
Wu
,
D.
Wu
,
W.
Yang
, and
L.
Luo
,
J. Mater. Sci. Technol.
72
,
189
(
2021
).
34.
M.
Zhang
,
Z.
Liu
,
L.
Yang
,
J.
Yao
,
J.
Chen
,
J.
Zhang
,
W.
Wei
,
Y.
Guo
, and
W.
Tang
,
Crystals
12
,
406
(
2022
).
35.
C.
Wu
,
F.
Wu
,
H.
Hu
,
S.
Wang
,
A.
Liu
, and
D.
Guo
,
Mater. Today Phys.
28
,
100883
(
2022
).
36.
37.
Q.
He
et al,
Appl. Phys. Lett.
110
,
093503
(
2017
).
38.
P. N.
Butenko
,
M. E.
Boiko
,
L. I.
Guzilova
,
V. M.
Krymov
,
S. V.
Shapenkov
,
M. D.
Sharkov
,
V. N.
Verbitskii
,
A. A.
Zarichny
, and
V. I.
Nikolaev
,
J. Cryst. Growth.
630
,
127597
(
2024
).
39.
G. K.
Williamson
and
W. H.
Hall
,
Acta Metall.
1
,
22
(
1953
).
40.
M. E.
Boiko
,
M. D.
Sharkov
,
A. M.
Boiko
,
S. G.
Konnikov
,
A. V.
Bobyl
, and
N. S.
Budkina
,
Tech. Phys.
60
,
1575
(
2015
).
41.
H.
Zhong
et al,
J. Phys. Chem. Lett.
14
,
6702
(
2023
).
42.
S. A.
Bereznaya
,
R. A.
Redkin
,
V. N.
Brudnyi
,
Y. S.
Sarkisov
,
X.
Su
, and
S. Y.
Sarkisov
,
Crystals
13
,
1562
(
2023
).
43.
X.
Chen
et al,
ACS Appl. Mater. Interfaces
11
,
7131
(
2019
).
44.
S. K.
Cheung
and
N. W.
Cheung
,
Appl. Phys. Lett.
49
,
85
(
1986
).
45.
L.
Du
et al,
IEEE Electron Device Lett.
40
,
451
(
2019
).
46.
Z.
Hu
,
H.
Zhou
,
K.
Dang
,
Y.
Cai
,
Z.
Feng
,
Y.
Gao
,
Q.
Feng
,
J. F.
Zhang
, and
Y.
Hao
,
IEEE J. Electron Devices Soc.
6
,
815
(
2018
).
47.
K.
Sasaki
,
M.
Higashiwaki
,
A.
Kuramata
,
T.
Masui
, and
S.
Yamakoshi
,
IEEE Electron Device Lett.
34
,
493
(
2013
).
48.
M.
Xian
,
C.
Fares
,
F.
Ren
,
B. P.
Gila
,
Y. T.
Chen
,
Y. T.
Liao
,
M.
Tadjer
, and
S. J.
Pearton
,
J. Vac. Sci. Technol. B
37
,
061201
(
2019
).
49.
J.
Yang
,
S.
Ahn
,
F.
Ren
,
S. J.
Pearton
,
S.
Jang
,
J.
Kim
, and
A.
Kuramata
,
Appl. Phys. Lett.
110
,
192101
(
2017
).
50.
K.
Konishi
,
K.
Goto
,
H.
Murakami
,
Y.
Kumagai
,
A.
Kuramata
,
S.
Yamakoshi
, and
M.
Higashiwaki
,
Appl. Phys. Lett.
110
,
103506
(
2017
).
51.
X.
Lu
,
X.
Zhang
,
H.
Jiang
,
X.
Zou
,
K. M.
Lau
, and
G.
Wang
,
Phys. Status Solidi A.
217
,
1900497
(
2020
).
52.
A. M.
Armstrong
,
M. H.
Crawford
,
A.
Jayawardena
,
A.
Ahyi
, and
S.
Dhar
,
J. Appl. Phys.
119
,
103102
(
2016
).
53.
D. Y.
Guo
,
Z. P.
Wu
,
Y. H.
An
,
X. C.
Guo
,
X. L.
Chu
,
C. L.
Sun
,
L. H.
Li
,
P. G.
Li
, and
W. H.
Tang
,
Appl. Phys. Lett.
105
,
023507
(
2014
).
54.
A. S.
Pratiyush
,
Z.
Xia
,
S.
Kumar
,
Y.
Zhang
,
C.
Joishi
,
R.
Muralidharan
,
S.
Rajan
, and
D. N.
Nath
,
IEEE Photonics Technol. Lett.
30
,
2025
(
2018
).
55.
D. H.
Vieira
,
N.
Badiei
,
J. E.
Evans
,
N.
Alves
,
J.
Kettle
, and
L.
Li
,
IEEE Trans. Electron Devices
67
,
4947
(
2020
).
56.
T.
Zhang
et al,
Nanoscale Res. Lett.
15
,
163
(
2020
).
57.
P.
Mukhopadhyay
and
W. V.
Schoenfeld
,
J. Vac. Sci. Technol. A.
38
,
013403
(
2020
).
58.
S.
Wang
,
C.
Wu
,
F.
Wu
,
F.
Zhang
,
A.
Liu
,
N.
Zhao
, and
D.
Guo
,
Sens. Actuator, A
330
,
112870
(
2021
).
59.
T.
Oshima
,
T.
Okuno
,
N.
Arai
,
N.
Suzuki
,
H.
Hino
, and
S.
Fujita
,
Jpn. J. Appl. Phys.
48
,
011605
(
2009
).