The heterostructures described here were prepared by solid‐state diffusion from a mixture of CdTe and HgTe powders into a wafer of single‐crystal CdTe. The composition profiles as measured with an electron‐beam microprobe show that 100 μ wide transition regions can be achieved. These profiles are consistent with published results on diffusion between bulk HgTe and bulk CdTe. Increasing the proportion of HgTe in the powder shifts the optical absorption edge from a wavelength of 0.8 μ (the value for bulk CdTe) to beyond the 15 μ limit of the measuring instruments. The photoelectromagnetic (PEM) effect shows a fairly flat spectral sensitivity for wavelengths between 1 and 5 μ. The photovoltaic response shows an anomalous exponential dependence on the photon energy, believed to be due to an undesirable p‐n junction caused by cadmium vacancy formation. Theoretical models are derived for both effects.

Topics
Heterostructures, P-N junctions, Optical absorption, Electron beams, Photovoltaics, Microprobe, Semiconductors
1.
R. L.
Anderson
,
Solid State Electron.
5
,
341
(
1962
).
Google Scholar
Crossref
Search ADS
 
2.
P.
Emtage
,
J. Appl. Phys.
33
,
1950
(
1962
).
Google Scholar
Crossref
Search ADS
 
3.
G. Almasi, MIT Energy Conversion and Semiconductor Laboratory Semiannual Technical Summary Rept. No. 3, NASA Grant NsG 496 (part), pp. 1–51, (Nov. 1964).
4.
H.
Kroemer
,
RCA Rev.
18
,
332
(
1957
).
Google Scholar
 
5.
J.
Tauc
,
Rev. Mod. Phys.
29
,
308
(
1957
).
Google Scholar
Crossref
Search ADS
 
6.
B. Segall and E. Pell, GE Research Laboratory Rept. No. 62‐RL‐3051G (June 1962).
7.
P. Aigrain (private communication).
8.
A.
Fortini
 and
J. P.
Saint‐Martin
,
Phys. Status Solidi
3
,
1039
(
1963
).
Google Scholar
Crossref
Search ADS
 
9.
M.
Wolf
,
Proc. IRE
48
,
1246
(
1960
).
Google Scholar
Crossref
Search ADS
 
10.
D.
DeNobel
,
Philips Res. Rept.
14
,
361
 
and
(
1959
).
Google Scholar
 
11.
A. J. Strauss, T. C. Harman, J. G. Mavroides, D. H. Dickey, and M. S. Dresselhaus, in Proceedings of the International Conference on Semiconductor Physics, Exeter, 1962, p. 703.
12.
W.
Lawson
,
S.
Nielsen
,
E.
Putley
, and
A.
Young
,
J. Phys. Chem. Solids
9
,
325
(
1959
).
Google Scholar
Crossref
Search ADS
 
13.
H.
Rodot
 and
J.
Henoc
,
Compt. Rend. Acad. Sci.
256
,
1954
(
1963
).
Google Scholar
 
14.
F.
Bailly
,
G.
Cohen‐Solal
, and
Y.
Marfaing
,
Compt. Rend. Acad. Sci.
257
,
103
(
1963
).
Google Scholar
 
15.
G.
Cohen‐Solal
et al.,
Compt. Rend.
257
,
863
(
1963
).
Google Scholar
 
16.
M. R.
Lorenz
 and
R. E.
Halsted
,
J. Electrochem. Soc.
110
,
343
(
1963
).
Google Scholar
Crossref
Search ADS
 
17.
J. W. Conley, MIT Sc.D. thesis (February 1965).
18.
R. E. Nelson, MIT Sc.D. thesis (May 1961).
19.
J. Blair, MIT Electron. Syst. Laboratory, Scientific Rept. No. 2, Contr. No. AF 19 (604)‐4153, June 1960.
20.
R. E. Ogilvie, in Introduction to Electron Beam Technology, R. Bakish, Ed. (John Wiley & Sons, Inc., New York, 1962), pp. 413–431.
21.
G. S.
Almasi
,
J.
Blair
,
R. E.
Ogilvie
, and
R. J.
Schwartz
,
J. Appl. Phys.
36
,
1848
(
1965
).
Google Scholar
Crossref
Search ADS
 
22.
Actually, further experiments in which the HgTe and CdTe slabs were separated by a void space indicate that the HgTe is transported to the CdTe surface in the vapor phase, and that subsequent diffusion takes place between the layer of HgTe formed in this way and the CdTe substrate. (M. Rodot, private communication.) This is most probably happening in the experiments of this study also. On several of our samples, twin line patterns visible in the CdTe “substrate” before diffusion were reproduced in the HgTe layer, which indicates that the process is epitaxial.
23.
W. Jost, Diffusion in Solids, Liquids, and Gases (Academic Press Inc., New York, 1960).
24.
P.
Kruse
,
M.
Blue
,
J.
Garfunkel
, and
W.
Saur
,
Infrared Phys.
2
,
53
(
1962
).
Google Scholar
Crossref
Search ADS
 
25.
The sensitive area was arbitrarily chosen to be equal to the illuminated area, resulting in a minimum or “worse case” value for the sensitivity.
26.
All the data on V34 reported here were magnetic‐field dependent, and reversed sign when the magnetic field was reversed. Several samples exhibited a smaller photovoltage at contacts 3–4 even in the absence of an applied magnetic field. The spectral response of this photovoltage was quite similar to the PEM voltage, as was its frequency response. It is believed that this effect arises when the diffusion interface and the back face of the sample are not parallel.
27.
Photovoltages arising from barriers in CdTe should be affected by photons with energy above 1.5 eV (the CdTe bandgap), but not by those with energy below 1.5 eV.
28.
W.
Schottky
,
Z. Physik
118
,
539
(
1942
).
Google Scholar
Crossref
Search ADS
 
29.
For more details, see G. S. Almasi, MIT Ph.D. Thesis (November 1966), also available as MIT Center for Space Res. Scientific Rept. No. 2 on NASA Grant NsG 496 (part), November 1966.
30.
A. K. Jonscher, Principles of Semiconductor Device Operation (John Wiley & Sons, Inc., New York, 1960).
31.
Cf. Eq. 4.07 of Ref. 8.
32.
A more general analysis in which finite values of the optical absorption coefficient α were considered and photon absorption was allowed wherever EG⩽hv did not yield significantly different results. See Ref. 29 for details.
33.
R. A. Hinrichs, MIT B.S. Thesis (June 1963).
34.
R. E. Halsted, D. T. F. Marple, and B. Segall, Fifteenth Quarterly Progress Report, ARL Contr. No. AF‐33 (616)‐8264 (April 1965).
35.
B. L. Crowder (private communication).
This content is only available via PDF.
© 1968 The American Institute of Physics.
1968
The American Institute of Physics
You do not currently have access to this content.