Plasma Passivation Scheme for III–V Compound Semiconductor Surfaces

Abstract

Passivation of III–V compounds, especially GaAs, is still a major problem. Surface mechanisms related to stoichiometry defects (free As formation, vacancies) play an important role in the detrimental effects observed on GaAs devices (interface traps, leakage currents, parasitic transients …).

We first analyze the phenomena occuring at GaAs (100) surfaces exposed to several (H₂, N₂) multipolar plasmas, with the following methods:

• in situ study of the surface morphology and roughness using ellipsometry and electron diffraction

• chemical analysis using photoemission and Auger spectroscopy

• electrical analysis in situ (Fermi level position deduced from photoemission, work function measurements) or ex situ (device characterization, C(V) analysis).

Using H₂ based plasma treatments, a complete cleaning (oxide and contamination removal) can be obtained at moderate (below 200 °C) temperatures. This process, associated with surface nitridation and dielectric deposition, yield improved surface properties (lower recombination velocity and reduction of devices parasitic effects).

The case of Ga_1−xIn_xAs (100) surfaces (with x varying from 0 to 0.53)is then discussed and a comparative study is given, indicating that native nitridation may also be a good solution, in this case.