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 subcollector, 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 InxGa1-xAsyP1-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 InxGa1-xAsyP1-y formation by the optimization of the growth temperature and the gas switching sequence time. An effective 20 angstrom InGaP etch-stop layer was grown at 575 degrees C with interruption time of 3 s. Both STEM and PL data proved that the intermixing InxGa1-xAsyP1-y layer was eliminated and from the selective etching experiment, this 20 angstrom InGaP layer can stand 45 s etching by the H3PO4:H2O2:H2O = 1:1:20 solution. (c) 2005 Elsevier B.V. All rights reserved.