By monitoring photoluminescence (PL) in real time and in situ, hydrogen plasma operating conditions have been optimized for surface passivation of native-oxide-contaminated GaAs. PL enhancement is critically dependent on exposure time and pressure because of competition between plasma passivation and damage. Optimal exposure time and pressure are inversely related; thus, previous reports of ineffective passivation at room temperature result from overexposure at low pressure. Plasma treatment is effective in removing As to leave a Ga-rich oxide; removal of excess As increases the photoluminescence yield as the corresponding near-midgap-state density is reduced. Passivation is stable for more than a month. These results demonstrate the power of real time monitoring for optimizing plasma processing of optoelectronic materials.
Absolute concentrations of ground state atomic hydrogen are determined by two-photon absorption laser-induced fluorescence in a pure hydrogen rf discharge. Axial concentration profiles obtained across the interelectrode space show a relatively constant concentration (of the order of 1014 atoms/cm3) in the region around the center of the discharge until it decreases sharply within 3–4 mm of each metal electrode surface. In addition, the temporal evolution of the atomic concentration is monitored by means of a pulsed discharge from short times to the establishment of a steady-state concentration. We present a model according to which the formation and decay of the distribution of atomic hydrogen is dominated by diffusion from the production regions towards both the center of the discharge and the metallic electrode surfaces where H atoms are absorbed.
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