Numerical calculations of the powder pattern of the central component shifted by the second-order nuclear quadrupole interaction in solids have been performed for various values of the asymmetry parameter, η. Shape functions have been obtained in units of (νQ2/6νL) (a—¾) for η=0.1, 0.2, ···, 1.0, at 0.1 intervals. Also, positions of special points such as infinities and steps of the shape function have been determined as functions of η. Effects of the dipolar broadening of the single-crystal resonance upon powder patterns have been estimated for the case of η=0.5. Influences of anisotropic magnetic shift were also discussed on powder patterns obtained experimentally. These relations are useful for simple and rapid determinations of η and νQ from the second-order powder pattern.
Distributed-feedback GaAs-GaAlAs diode lasers with separate optical and carrier confinement have been successfully operated under dc bias up to room temperature. They lased in a single longitudinal mode with a threshold current density of 0.94 kA/cm2 at 170 K and 3.5 kA/cm2 at 300 K.
Lasing spectra of a transverse-mode-stabilized AlGaAs laser of a channeled-substrate planar structure have been investigated. These lasers, which oscillate in the fundamental transverse mode, reproducibly operate in a single longitudinal mode. In addition, their linewidth is as narrow as or smaller than 30 MHz when the injection current is ∼1.2 times above threshold. The intensity distribution and excitation dependence of a nonlasing longitudinal mode have been found to be more complicated than expected from a simple theory: sizable dips have been observed in the envelope function, and nonlasing modes have been found to decrease as the injection current is increased above threshold. Furthermore, hysteresis has invariably been observed in the lasing-wavelength–vs–device-temperature (or dc current) characteristics. These behaviors are believed to reflect a slightly inhomogeneous nature of the gain spectrum because of a finite thermalization time of injected carriers, as discussed recently by Yamada and Suematsu.
A nonradiative dark region along a surface ripple is observed in optically and electrically excited GaP LPE layers. The region originates from the substrate interface and terminates at the ridge of the surface ripple. It is clearly distinguishable from the known one caused by dislocation in its features. The p-n junction breakdown voltage in this region is lower than that in the radiative region in a LPE layer. This fact suggests that in liquid-phase epitaxy an impurity concentrated region is formed in the growing process of surface ripples. The existence of the region contributes to the deterioration of the characteristics of devices using thin LPE layers.
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