James Comas

Etch Rates and Selectivities of Citric Acid/Hydrogen Peroxide on GaAs , Al0.3Ga0.7As , In0.2Ga0.8As , In0.53Ga0.47As , In0.52Al0.48As , and InP

Etching studies involving citric acid/hydrogen peroxide (C 6 H 8 O 7 :H 2 O 2 ) at volume ratios from 0.5: 1 to 50: 1 were found to provide good selective etching of various III-V semiconductor materials grown on GaAs and InP substrates using molecular beam epitaxy. Both selective and uniform (nonselective) etching regions were found between these material systems by choosing different concentration volume ratios of citric acid/hydrogen peroxide (χC 6 H 8 O 7 :1H 2 O 2 )

Study of ion‐implantation damage in GaAs:Be and InP:Be using Raman scattering

The Raman spectra of GaAs and InP implanted with Be ions with fluences ranging from 5×1012 to 1×1016 cm−2 were investigated. A marked difference in the behavior of the TO and LO modes with respect to broadening with fluence was observed and the results indicate that this is caused by frequency dependent anharmonic damping constants. The Raman spectra of high fluence samples are interpreted in terms of disorder‐induced first‐order Raman spectra due to phonons with nonzero wave vectors. The similarities between our ‘‘Reduced Raman Spectra’’ of the disordered form and the theoretical one‐phonon density of states, are presented without introducing Gaussian broadening as suggested by earlier authors studying amorphous materials. The observations support the conclusion that the form essentially retains the short‐range order of the crystalline phase; the phonon spectrum of the crystal is largely determined only by near‐neighbor interactions; and the existence of a frequency‐dependent coupling constant for the sc...

Diffusion studies of Be-implanted GaAs by SIMS and electrical profiling☆

Abstract Secondary ion mass spectrometry (SIMS) has been used with differential resistivity and Hall effect measurements to study the 900°C diffusion of implanted Be in GaAs. Some outdiffusion of Be into the Si3N4 encapsulant occurs for surface Be concentrations above 1 × 1018 cm−3. However, excellent agreement between the electrical and atomic profiles indicates that 85–100% of the Be remaining after annealing is electrically active. The concentration-dependent diffusion observed for implanted Be in GaAs was not significantly altered in experiments using hot substrate implants, two-step anneals, or annealing with Ga and As overpressure.

Composition, Chemical Bonding, and Contamination of Low Temperature SiO x N y Insulating Films

The stoichiometry and contamination of low temperature layers grown by the pyrolytic decomposition of silane in an ammonia‐ and oxygen‐rich atmosphere on and Si substrates are reported. The chemical composition and chemical bonding properties of the films have been analyzed by Auger, nuclear reaction analysis, optical, Rutherford backscattering, and SIMS techniques. Capacitors were fabricated on Si and substrates, and the electrical characteristics were measured. The layers exhibited physical characteristics similar to those of thermally grown layers. Analysis of the films indicated a uniform distribution of Si and O throughout the films. The N concentration measured in the films ranged from 1 to 3% of the O concentration, depending on the growth parameters. The optical results indicated some evidence of small amounts of Si‒N and N‒H bonding. All films grown on Si substrates in the presence of or on substrates had In and Sb contamination throughout, with the In and Sb content increasing from the film/substrate interface to the surface.

Channeling and random equivalent depth distributions of 150 keV Li, Be, and B implanted in Si

Atomic depth distributions for the low atomic number ions 73Li, 94Be, and 115B implanted into channeled and random equivalent orientations in crystalline silicon have been studied. The atomic depth distributions were obtained by secondary ion mass spectrometry measurements on samples implanted to fluences low enough to preserve the integrity of the channeling components. All implants were performed at 150 keV into the 〈100〉 and 〈110〉 directions and into the (111) random equivalent orientation of float‐zoned (low‐oxygen) silicon crystals. The results show that in the three orientations studied the ion ranges decrease with increasing atomic number Z1. This is indicative of the strong increase in electronic stopping Se for the Z1=3, 4, 5 sequence. The increase in ion penetration in the channeling orientation is greater with decreasing Z1 in the lower electronic stopping 〈110〉 channel than in the higher electronic stopping 〈100〉. Values of Se determined for channeled Li and Be at an ion velocity of 1.5×108 cm...

Beryllium and sulfur ion-implanted profiles in gaas

Atomic profiles of ion-implanted Be and S in GaAs have been measured as a function of implant fluence and annealing temperature. Concentration versus depth profiles were ob-tained by means of secondary ion mass spectrometry (SIMS) techniques. Pyrolytically deposited and sputter-coated Si02 and Si3N4 films were used as encapsulants for the 500 to 900° annealing study. Semi-insulating GaAs was implanted with 200 keV34S+ to fluences of 1 × 1014 and 52× 1014/cm2, and 100 keV9Be+ in the 1 × 1013 to 1 × 1015/cm2 fluence range. The S profiles did not change significantly after annealing at 800°C, although there was some skewing after annealing above 600°C. In contrast, the Be profiles showed significant changes and a decrease in the peak concentration for the ≥ 5 × 10T4/cm2 implants after a 700°C anneal. After a 800°C anneal the Be profile was essentially flat with a monotonic decrease from the surface into the implanted re-gion and a 900°C anneal caused a further decrease in the Be concentration. Profiles of Be implants of ≤ 1 × 1014/cm2 did not change significantly after annealing indicating that the higher fluence cases were related to solubility effects.

Depth profiles of aluminum and sodium near surfaces: Nuclear resonance method

Depth profiles of aluminum and sodium implanted into silicon carbide, silicon and silicon dioxide have been measured by means of sharp resonances in the reactions 27Al(p,γ)28Si and 23Na(p,γ)24Mg. The absolute number of impurity atoms has been determined and compared with that indicated by charge integration during implantation. Adjacent areas of some specimens have been measured by the Cameca ion-beam mass spectrometer and the nuclear resonance method; results are compared. A depth resolution of less than 20 A has been demonstrated for Al very near the surface of SiC. Information concerning the migration of sodium in SiO2 under ion bombardment is presented. Depth profiles are extracted from gamma-ray yield curves taking into account the beam energy distribution, the resonance shape, the average proton energy loss in the sample and the energy loss straggling.

Optical and electrical properties of boron‐implanted amorphous germanium thin films

Amorphous germanium films were implanted to high boron levels, ∼1021/cm3 peak concentrations. Before and after implantation the conductivity measurements fit the relation logσ∼T−1/4 and no evidence of intravalence absorption was observed indicating that the Fermi level was near the center of the band gap. Thermoelectric power measurements indicated that the samples were weakly n type before implantation and p type after implantation. The position of the fundamental absorption edge shifted to lower energy upon implantation and to higher energies upon subsequent anneals. Implanted recrystallized films were strongly p type, exhibited intravalence absorption, and had very low dc activation energies.

Interband transitions in molecular‐beam‐epitaxial AlxGa1−xAs/GaAs

Interband transition energies for AlxGa1−xAs layers grown by molecular‐beam epitaxy (MBE) techniques have been determined using the electrolyte electroreflectance (EER) technique. The observed data fit quadratic relations for E0, E0+Δ0, E1 and E1+Δ1 to describe variations of energy with composition. Although the x values were not accurately known, the internal consistency of the data is excellent. Given a single bowing parameter we show that accurate values of x can be determined. The EER technique can provide x values with an accuracy better than 0.02 and information on changes in x as small as 0.002. It is thus ideally suited for studying MBE materials.

Effects of annealing on profiles of aluminum implanted in silicon carbide

The effects of isothermal annealing on the profiles of heavy (4×1016 Al+/cm2 at 60 keV) implantations of Al in SiC were investigated by means of the 27Al(p,γ)28Si nuclear resonance technique. Annealing at 1400 °C for 15 min resulted in the apparent outdiffusion of about 30% of the implanted Al, an accumulation of Al at the surface, and a residual peak at the depth of the as−implanted profile. Subsequent annealing showed continued apparent outdiffusion with the release of Al from trapping sites as the rate−limiting process.