Optimization of the growth of the InGaP etch-stop layer by MOVPE for InGaP/GaAs HBT device application

Abstract

InGaP has high etching selectivity to GaAs. It can be used as the etch-stop layer to easily fabricate the InGaP/GaAs heterojunction bipolar transistors (HBTs). This process will also increase the uniformity and manufacturability of the HBT devices. However, the InGaP etch-stop layer will increase the energy barrier height that electrons have to overcome flowing from the collector to the sub-collector, which will decrease the DC current gain of the device (T. Kobayashi, K. Taira, F. Nakamua, H. Kawai, J. Appl. Phys. 65 (1989) 4898). Therefore, the InGaP etch-stop layer has to be thin enough not to affect the device performance. But the spontaneous formation of the In xGa 1− x As y P 1− y intermixing layer between GaAs/InGaP during the metal organic vapour-phase epitaxy (MOVPE) growth will affect the InGaP layer thickness needed as an effective etch-stop layer. In this paper, very thin InGaP layer was achieved with the suppression of In x Ga 1− x As y P 1− y formation by the optimization of the growth temperature and the gas switching sequence time. An effective 20 Å InGaP etch-stop layer was grown at 575 °C with interruption time of 3 s. Both STEM and PL data proved that the intermixing In x Ga 1− x As y P 1− y layer was eliminated and from the selective etching experiment, this 20 Å InGaP layer can stand 45 s etching by the H 3PO 4:H 2O 2:H 2O=1:1:20 solution.