Spectroscopic Characterization of Dry Etch-Induced Modification in Iii-V Semiconductors and Semiconductor Heterostructures

The effects of dry etching on the structural and electrical properties of III-V semiconductors and semiconductor heterostructures were studied using vibrational and electronic Raman spectroscopy and low and room temperature photoluminescence spectroscopy. The frequency, intensity, and lineshape of the dipole-allowed and dipole-forbidden longitudinal optic (LO) phonon as well as the dipole-forbidden transverse optic phonon were used to evaluate structural modification in doped and undoped material. The intensities and frequencies of the coupled LO phonon-plasmon modes relative to those of the unscreened LO phonon were used to probe changes in the surface space charge region and free carrier concentration. Photoluminescence peak energies, intensity, and lineshape were used to evaluate crystal quality and defect identity. Structural modification was investigated in GaAs etched in SiCl_4, SiCl_4 /SiF_4, and CH_4 /H_2 plasmas and sputtered in an Ar plasma. SiCl_4 and SiCl _4/SiF_4 etches both produced significant structural modification. CH _4/H_2 plasmas produced less structural modification, however, a highly disordered surface layer was still created. Electrical modification by the methane-based plasmas was found to depend weakly on the self-bias voltage and was confined to within ca. 125 A of the surface. The effects of reactive ion etching (RIE) in methane -based plasmas as well as sputtering in Ar and He plasmas on InP were investigated. In general, methane-based plasmas showed far less structural damage than sputtering. Samples sputtered in Ar plasmas exhibited the most structural modification, however, at larger bias voltages some structural modification was observed for methane-based etches (except CH _4/H_2 plasmas). Of the methane-based etches CH_4/H _2 and CH_4/H _2/Ar plasmas exhibited the least structural modification. Electrical modification was also seen to be more extensive with sputter etches than methane -based etches. Samples sputtered in He plasmas showed more electrical perturbations than samples sputtered in Ar plasmas. Methane -based etches did affect electrical properties of InP. No clear trends were observed, although, in general, CH _4/H_2 etches resulted in the largest depletion widths. The effects of HBr RIE and Ar sputtering on InGaAs and InAlAs were investigated. Ar sputtering of InGaAs resulted in significant structural modification. HBr-etching lead to significantly less structural modification, although some disorder was created by these etches. Ar sputtering of InAlAs also resulted in structural modification, although to a lesser degree than observed for InGaAs. Ar sputtering results in the formation of a high-donor density surface region, which leads to the creation of an electron accumulation layer in the near-surface region. A decrease in carrier concentration was observed to ca. 230 A in HBr-etched n^+-InAlAs. The presence and shifts of the coupled phonon -two-dimensional electron gas (2DEG) plasmon modes in InGaAs/InAlAs heterostructures were used to investigate the effects of HBr RIE on the 2DEG properties. Etch-induced 2DEG modification was greatly reduced when the InAlAs barrier thickness was increased from 75 A to 350 A. For the structures with the smallest barrier thicknesses the decrease in 2DEG concentration was more strongly dependent on increased etch times than increased self-bias voltage.