Tetsuro Nozu

Carrier Passivation in Heavily Doped GaAs:Be by Hydrogen Plasma

The electrical property around the surface of a heavily Be-doped p + GaAs layer exposed to hydrogen plasma has been investigated. The resistance around the surface has been made over six orders of magnitude larger by a 150 W and 10 min plasma exposure. Sheet carrier measurement with step etching has shown that the depth of the passivated front proceeds by diffusion. The time dependence of carrier removal has been found to have three distinct regions including a plateau. These regions have been explained by a 50 nm thick highly resistive layer which is formed within the first 1 minute during the plasma treatment prior to passivation due to hydrogen diffusion

Negative Transconductance in AlGaAs/GaAs Heterojunction Bipolar Transistors

Negative transconductance has been observed and analyzed for the first time in AlGaAs/GaAs HBTs when VBE is larger than 1.7 volts. A newly developed equivalent circuit model with an additional external base-emitter diode and a temperature-dependent resistor which corresponds to the intrinsic base resistance is proposed on the basis of experimental data for a pulse-biased I-V characteristic and temperature dependence of the sheet resistance for p-GaAs layers. Using this model, it is shown that negative transconductance is one of the novel characteristics in HBTs and is attributed to the drop in the input voltage across the intrinsic base resistance which increases with the input power through heat generation.