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

Abstract

Spectral response (SR) and optical characteristics of GaAs-based heterojunction phototransistors (HPTs) have been successfully predicted for the first time through an advanced absorption model presented in the present article. The model is based on the accurate prediction of photocarriers in the active layers of the phototransistor which, when related to the base current of transistor in forward active mode, enables the prediction of optical characteristics. The importance of collection efficiency in accurate SR modelling is highlighted and it is not considered unity like all the previous studies on HPTs. The layer dependence of the optical power absorption profile at near-bandgap wavelengths is also investigated and its generalisation as a single exponential has been refuted for GaAs-based HPTs. The measured results at 635, 780 and 850 nm show good agreement to the predicted results, validating the proposed theoretical model.

Design and Modeling of GeSn-Based Heterojunction Phototransistors for Communication Applications

“…Because the light is normally incident on the emitterbase junction, we do not consider the depletion of the emitter region. The optical flux absorption in the layers can be written as follows [36]:…”

“…Because the light is incident normally on the base-emitter interface, η can be written as follows [36]: Ideally, η can reach its maximum if the photon flux is fully absorbed by the base, collector, and the sub-collector layers of the HPT.…”

“…For an incident optical power of smaller than 20 µW, the relation between the optical power and the photocurrent is usually linear and the current gain is independent of the incident optical power, that is, no kink effect [21]. Under this assumption, the spectral optical responsivity of the Ge 1−x Sn x HPT can be calculated as follows [36]:…”

Modeling and analysis of the spectral response for AlGaAs/GaAs HPTs for short wavelength optical communication

“…The micrograph of fabricated device and the detailed device layer structure can be found elsewhere. 25 The HPT wafers under investigation were set on a four DC-probe station. The laser diode (LD) is aligned to a multimode optical fiber (50 lm core diameter) using collimating and focusing lenses.…”

Analysis on high speed response of a uni-traveling-carrier double hetero-junction phototransistor

“…In ROF systems, HPTs not only serve as the high-performance photo-detector part but also amplify or mix microwave or millimeter-wave sub-carrier. [1][2][3] Most of the HPTs reported in the past two decades were fabricated using the AlGaAs/GaAs, InGaP/GaAs or InP/InGaAs material structures, and always had one or two hetero junctions with the base region, the base/collector depletion region and the collector region as the absorption area. In the depleted zone between the base and collector, electron-hole pairs were generated and separated.…”