Characterisation of transparent ITO emitter contact InP/InGaAs heterojunction phototransistors

Abstract

The electrical, optical and spectral responses of optically transparent emitter InP/InGaAs heterojunction phototransistors (HPTs) fabricated using Indium Tin Oxide (ITO) are presented. These HPTs showed significantly increased optical responsivities while the electrical characteristics were similar to their respective opaque counterparts. Responsivities of 28A/W at 1310nm for the InPhGaAs HPTs were obtained. The spectral responses of these phototransistors were simulated and compared with the measured results and good correlation between the experiments and the theoretical models were obtained.

Spectral Response Modelling of Heterojunction Phototransistors for Short Wavelength Transmission

“…Referring to fig. 1, the flux propagation in different layers has been modelled by (13) and numerically shown in fig. 4.…”

“…In the present work the variation of absorption coefficient with doping is analysed and taken into consideration for the power absorption profile. In our earlier works [8] and [13], we presented a spectral response model for hetero-structures but this is only valid for relative measurement of spectral response and cannot be used for absolute responsivity measurements. In this paper, a modified formulation has been presented to accurately determine the absolute responsivity of HPTs.…”

“…Several models have already been developed for photodetectors and phototransistors [9]- [13]. In all these models, collection efficiency is taken as unity for the analysis which may not be the case for every detector.…”

Spectral response modelling of GaAs-based heterojunction phototransistors for short wavelength detection

“…Optical absorption is a distance-dependent parameter and hence a change in the origin (in the lower-limit of integral) is necessary for accurate prediction of SR. This modification has been proposed to the absorption model presented in our earlier work [13,14], which was only valid for relative SR estimation. The electron-hole pairs generated from photon absorption in the fully depleted collector layer will be swept across by a strong electric field towards the subcollector and base regions, respectively.…”

“…A key performance parameter of HPTs is their spectral response (SR), which is critical in their usage in optical applications. The modelling of SR for photodiodes has been extensively reported [9][10][11][12]; however, several attempts at modelling of SR of HPTs have been limited to a relative or normalised response [8,13,14]. The lack of success in the modelling of absolute SR is related to some simplistic assumptions taken from photodiodes and applying these to HPTs.…”