No abstract

We have built a particle analyzer capable of real-time detection and characterization of individual particles. Particle analysis is accomplished by pulsed laser ablation of a particle followed by time-of-fiight mass spectrometry of the resulting atomic and molecular ions. The detected ions are characteristic of a particle's

Structural and electrical damage imparted to InP and In0.72Ga0.28As0.6P0.4 (λg≂1.3 μm) surfaces during CH4/H2 reactive ion etching (RIE) have been examined. X-ray photoelectron spectroscopy was used to monitor changes in the surface chemistry, Rutherford backscattering spectrometry was used to measure crystallographic damage, and current-voltage and capacitance-voltage measurements were made to examine electrically active damage and its depth. Two classes of damage are observed: crystallographic damage originating from preferential loss of P (As) and/or ion bombardment-induced collision cascade mixing and, for p-type material, hydrogen passivation of Zn acceptors. Etching at 13.6 MHz, 60–90 mTorr, 10% CH4/H2, and bias voltages of ∼300 V contains gross (≳1%) damage as measured by RBS to within 40 Å and electrically active damage to within 200 Å of the surface. This is a factor of 3–6 shallower than other RIE processes operated below 10 mT with comparable or higher bias voltages. Acceptor passivation of both InP and InGaAsP, arising from the association of hydrogen with Zn sites, occurs to a depth of 2000 Å after RIE and causes a decrease in carrier concentration in this layer. The effect is reversed, however, by rapid thermal processing at temperatures between 350 and 500 °C.

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.

X-ray photoelectron spectroscopy (XPS) spectra have been obtained for TiNx, with x=0.25, 0.50, and 1.0, as determined by Rutherford backscattering (RBS) analyses, and with no detectable oxygen content. We find the shape of the Ti 2p transition to be strongly dependent upon the nitrogen content, and interpret the spectrum as a mixture of Ti and TiN. TiN1.0 samples with varying oxygen content were also examined, and the oxygen content serves to increase the background step in the Ti 2p transition. Angle resolved measurements indicate that the inelastic scattering due to oxygen is superimposed over an intrinsic satellite structure in the Ti 2p transition. Atom ratios, N/Ti, cannot be accurately determined by XPS without standardization. The binding energy of the Ti 2p3/2 transition occurs at 454.5 eV and the N 1s transition occurs at 396.7 eV. The oxygen that is present in TiN at concentrations up to 12 at. % is most likely bound to Ti as TiO rather than TiO2. Valence band measurements agree well with previous reports.