The effect of aperture layout design on the multi-GHz operation of light-emitting transistors

Abstract

The base current ( I B ) plays a key role in the transistor since its discovery (16 December 1947, Bardeen and Brattain). It separates the low impedance input (emitter) from the high impedance output (collector), thus yielding a “transfer resistor.” Recently, III-V semiconductor material has been fabricated as a heterojunction bipolar transistor (HBT) which can operate as a high speed device. The HBT can be modified and operated as a three-port light-emitting device (an electrical input, electrical output, and a third port optical output) by incorporating one or more quantum wells in the base region, thus becoming a heterojunction bipolar light-emitting transistor (LET). In the present work, we have designed different sizes of emitter diameter D E and base diameter D B of InGaP/GaAs LETs in aperture layout design. Through different layout designs, the LETs exhibit different electrical current gain (β= I C /I B ) and optical light output due to different carrier recombination processes in the transistor base region. By reducing the lateral emitter size from 18 to 13 μm, β increases due to the higher injection current densities and better confinement of the radiative recombination in the base region. Moreover, β increases when reducing the base diameter from 27 to 22 μm with fixed emitter diameter. The effective carrier recombination lifetime, τ rec , can be estimated from dc analysis and rf measurement (small-signal modulation).We have obtained multi-GHz spontaneous light modulation of LETs, and the device performance is closely related to different layout designs with different device parasitics.