Resonant cavity enhanced AlGaAs/GaAs heterojunction phototransistors with an intermediate InGaAs layer in the collector

Abstract
Gain and spectral response of heterojunction phototransistors (HPTs) having a thin (0.1 μm) InGaAs strained absorbing layer in the collector has been investigated. Low dark current ∼ 5 pA (1×10−8 A/cm2) and large optical gain as high as 500 were observed. A resonant cavity composed of an AlAs/GaAs buried mirror structure (reflectivity R=0.9) and the epilayer surface (R=0.3) was used to enhance the otherwise small quantum efficiency η (at InGaAs absorption wavelength). For a 1000 Å absorbing layer an improvement of η from 6.7 to 43% (6.4-fold) was demonstrated, in agreement with calculations, through the spectral analysis of the HPTs with and without resonant cavities.