Jun-Ichi Umeda

Nuclear Magnetic Resonance Powder Patterns of the Second‐Order Nuclear Quadrupole Interaction in Solids with Asymmetric Field Gradient

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.

GaAs–Ga1−xAlxAs double‐heterostructure distributed‐feedback diode lasers

We report laser oscillation at 80–100°K in electrically pumped GaAs–Ga1−xAlxAs double‐heterostructure distributed‐feedback diode lasers. The feedback for laser oscillation was provided by a corrugated interface between the active GaAs layer and the p‐Ga1−xAlxAs layer. The lowest threshold current density was 2.5 kA/cm2 in pulsed operation. The wavelength of laser emission was 8112 A at 82°K with a half‐width of less than 0.3 A. The temperature dependence of the laser wavelength was found to be smaller than that of the conventional Fabry‐Perot laser.

Nonradiative dark regions along surface ripples in GaP LPE layers

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.

Room Temperature Operation of Distributed Feedback Diode Lasers with Separate Carrier and Optical Confinement

Distributed feedback GaAs-GaAlAs diode lasers with a separate confinement heterostructure are fabricated and operated successfully at room temperature under pulse and DC bias. A threshold current density of 3.4 kA/cm2 is obtained at junction temperature Tj=320 K. The lasing spectra are examined closely, and single longitudinal mode oscillation is ascertained up to twice the threshold current density.