Carrier depletion effects and heat generation in thermal modeling of GaInP/p-GaAs heterojunction bipolar transistors

Usually, thermal modeling of semiconductor devices is based on a heuristic reasoning for appropriating the heat generation areas in the active device regions, involving several a priori assumptions. This paper establishes the rationale for appropriating suitable regions inside the active device as sources for heat generation - Joule heat, Thomson heat and Recombinant heat, along with a brief discussion of the causes for their generation. Moreover, the primary heat generation regions have been identified in a nGaInP-Si/pGaAs-C heterojunction bipolar transistor (HBT), through analytical determination of the depletion regions in both the GaInP emitter and the n-GaAs collector, based on ab-initio calculations. Energy band diagrams have been developed, and a detailed thermal model of a 2 μm×16.5 μm emitter device with six emitters has been developed using Finite Difference Analysis (FDA). Additionally, the temperature profile across the active region of the device was characterized using emission spectroscopy. Close agreement was found between the results from the thermal model and physical measurements.