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In this report, the optical frequency responses of InGaP/GaAs heterojunction bipolar light-emitting transistors are measured and analyzed using electrical small-signal equivalent circuit models under common-emitter, common-base, and common-collector configurations. Different optical modulation amplitudes and bandwidths, f3 dB, are obtained due to different input impedances and electrical transfer functions. The optical response of light-emitting transistors is able to be “tuned” by different input ports due to unique three-terminal characteristics along with carrier-photon conversion in the base region. From microwave analyses, identical “intrinsic” optical responses can be determined under three configurations at same DC bias condition.

The Franz-Keldysh (FK) absorption at the basecollector junction of a transistor laser (TL) is inevitable because of the reverse bias therein. The bias condition, thus, plays a crucial role in the determination of internal loss of TLs. In this study, effects from various facet coatings of edge-emitting TLs on the internal loss (α int ), which is influenced by the FK absorption, are investigated. Experimental analyses on the electrical and optical characteristics of these TLs at various temperatures are presented. The α int of different coated devices at various bias voltages are then extracted from their light-versus-current curves. We demonstrate that the internal loss resulted from the FK absorption is bias dependent, and therefore tunable. By contrast, the intense field inside the cavity with highly reflective coatings on both facets may saturate the FK absorption and make it less bias controllable. Index Terms-Transistor laser, Franz-Keldysh absorption, laser internal loss.1077-260X

In this report, the modulation of current gain of InGaP/GaAs light-emitting transistors under different ambient temperatures are measured and analyzed using thermionic emission model of quantum well embedded in the transistor base region. Minority carriers captured by quantum wells gain more energy at high temperatures and escape from quantum wells resulting in an increase of current gain and lower optical output, resulting in different I-V characteristics from conventional heterojunction bipolar transistors. The effect of the smaller thermionic lifetime thus reduces the effective base transit time of transistors at high temperatures. The unique current gain enhancement of 27.61% is achieved when operation temperature increase from 28 to 85 °C.

In this paper, we demonstrate the improvement of cutoff frequency of the light-emitting transistor (LET) due to quantum well (QW) band-filling phenomenon (i.e., saturation) along with the carrier capturing and escaping processes in the base region. Through microwave measurement followed by smallsignal model analysis, we observe that the base transit time, τ t , of the LET is reduced evidently from 90 to 20 ps when the collector current density increases from 2.43 to 34.9 kA/cm 2 . The reduction of τ t via saturation effect can be explained by the electroluminescence spectrum and thermionic emission theory of QW.Index Terms-Carrier capture and escape time, light-emitting transistor (LET), quantum well (QW) saturation.