Far-infrared magnetospectroscopy has been carried out on shallow donor impurities doped in the central region of GaAs quantum wells in o GaAs-Al x Gai_ x As multiple-quantum-well structures. Quantum-well widths between 80 and 450 A were investigated. Results are in very good agreement with recent effective-mass calculations for isolated impurities at the center of GaAs quantum wells.

Etching studies involving citric acid/hydrogen peroxide false(C6H8O7:H2O2false) 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 normalGaAs and normalInP 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 false(χC6H8O7:1H2O2false) . Etchant selectivities, defined as a ratio of the etch rates, for the normalGaAs‐normalbased materials were measured to be as high as 116 for normalGaAs/As0.3Ga0.7AS and 120 for In0.2Ga0.8normalAs/Al0.3Ga0.7normalAs . In addition, the normalInP system had selectivities of approximately 60 and 100 for In0.53Ga0.47normalAs/In0.52Al0.48normalAs and In0.52Al0.48normalAs/normalInP , with the highest selectivity of 473 found for In0.53Ga0.47normalAs/normalInP . The citric acid/hydrogen peroxide system can be used as a stop etch for normalInP‐normalbased devices, as normalInP is virtually unaffected by this etchant. Finally, citric acid/hydrogen peroxide can be used to preferentially etch these materials through a photoresist mask, since it does not erode photoresist at any volume ratio.

The optical modulation technique of photoreflectance (PR) has been applied to characterize the interband transitions in GaAs/AlGaAs multiple quantum wells (MQW) and modulation-doped heterojunctions at room temperature. The spectra of the MQW show ‘‘derivativelike’’ reflectance features due to allowed interband transitions from heavy and light hole subbands to conduction subbands, and the E0(Γ8,v→Γ6,c) transitions of the AlGaAs layers. Our data are consistent with a square well calculation using a conduction-band offset of 60% of the band-gap discontinuity. For modulation-doped heterojunctions, a correlation is observed between a PR feature approximately 18 meV above the GaAs fundamental gap and the presence of a two-dimensional electron gas.

Phys. Status Solidi 25, 92 (1968). 600 'C. Comparison is made with previously reported fast-neutron irradiations and the present work. Point defects on the cation sublattice, such as the V center, were sought for but determined not to be present in sufficient concentration to be detected by the presence of the well-known 2.3-eV optical-absorption band.

The Raman spectra of GaAs and InP implanted with Be ions with fluences ranging from 5 X 10 12 to I X 10 16 cm -2 were investigated. A marked difference in the behavior of the TO and La 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 nearneighbor interactions; and the existence of a frequency-dependent coupling constant for the scattering intensity at least in the low frequency region.