Study of a-Si:H emitters for efficient carrier injection in GaAs bipolar devices

Experimental and theoretical results are presented concerning the application of a wide gap amorphous silicon layer to improve the injection efficiency into GaAs regions. A 30 nm a-Si:H film is grown by low temperature (T=270°C) plasma enhanced chemical vapour deposition and has an energy gap of 1.8 eV, which is 0.4 eV larger than that of the underlying crystalline GaAs. The pin diode which is fabricated has device quality rectifying properties and a reverse breakdown voltage of 120 V. When operated as a current switch it has a reverse recovery time of 20–30 ns, largely determined by the minority carrier recombination in the GaAs intrinsic layer. The theoretical analysis of the device, based on a numerical physical simulator, shows that the density of states at the interface affects the forward bias voltages and currents.