Role of carrier depletion effects and material properties in advanced microscale thermal modeling of GalnP/pGaAs heterojunction bipolar transistor (HBT) devices

Ab-initio calculations were performed to determine the width of the depletion regions in a n-GalnF‘/p GaAs heterojunction bipolar transistor (HBT), by constructing the energy band diagmms for the GalnP emitter, and the ‘degenerate’ pdoped GaAs base region. The depletion regions were established as the regions of primary heat generation inside the HBT. A detailed thermal model of a 2pm x 16.5pm emitter device with six emitters has been developed using Finite Difference Analysis (FDA). Carc has been taken to incorporate the contact metallization and fine geometry, including the representative collector and base mesa structures. The thermal conductivity of the materials involved were carefully established as functions of temperature. 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 mcasurements. 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.