Surface treatment for enhancing current gain of AlGaAs/GaAs heterojunction bipolar transistor

Abstract

This paper presents a method of surface treatment for improving the current gain of an AlGaAs/GaAs heterojunction bipolar transistor (HBT). Several recipes for GaAs surface treatment, including each and several combinations of the H 2 plasma, NH 3 plasma, and (NH 4) 2S x chemical treatments are examined. The lowest SiO 2/GaAs interface state density of 1.23 × 10 10 cm −2 eV −1 is obtained when the GaAs surface is treated in sequence with (NH 4) 2S x :H 2O=1:1 solution, H 2 plasma, and NH 3 plasma. The current gain of an AlGaAs/GaAs HBT, whose extrinsic base surface is treated with this recipe, is enhanced at a low collector current by a factor of 2.5 from that without surface treatment. The maximum current gain is also enhanced by a factor of 1.37.