$InAlGaAs∕InP$ light-emitting transistors operating near $1.55μm$

Light-emitting transistors (LETs) operating at around $1.55μm$ were investigated using $InP∕InAlGaAs$ heterostructures grown by metal organic chemical vapor deposition. By incorporating InGaAs quantum wells (QWs) in the base region of the $N-InP∕p-InAlGaAs∕N-InAlAs$ heterojunction bipolar transistors, LET structures were achieved with a current gain of 45 and light emission at a wavelength of $1.65μm$⁠. The light output was found to be dependent on the base current. The larger the number of QWs incorporated in the base of the LETs, the larger the light output, with correspondingly reduced current gain. Secondary ion mass spectroscopy shows that the $p$-type dopant, zinc (Zn), which is commonly used in the growth of InAlGaAs, diffuses into the emitter and the base active QW region, leading to compromised electrical performance and light output intensity. Increasing the Zn doping level in the barrier layers of the QW structure causes the photoluminescence efficiency to decrease rapidly. Consequently, an alternative low-diffusivity dopant, carbon (C), was studied and a LET with a C-doped base was grown and fabricated. The highest light output was demonstrated for the C-doped LETs owing to the improved quality of the active layer.