A. Niwa

GaInNAs: A Novel Material for Long-Wavelength-Range Laser Diodes with Excellent High-Temperature Performance.

We propose a novel material, GaInNAs, that can be formed on GaAs to drastically improve the temperature characteristics (T0) in long-wavelength-range laser diodes. The feasibility of our proposal is demonstrated experimentally.

Dependence of optical gain on crystal orientation in surface‐emitting lasers with strained quantum wells

We analyze theoretically optical gains in vertical‐cavity surface‐emitting lasers (VCSELs) for various crystal orientations. The calculation based on the multiband effective‐mass theory takes into account the effects of anisotropy and nonparabolicity on the valence subband dispersion. It is found that in VCSELs employing InGaAs/InP strained quantum wells (QWs) with non‐(001) orientations except (111), the polarization in the QW plane can be controlled and high gains are obtained. In particular, the gains in VCSELs with (NN1)‐oriented (N≥2) strained QWs are markedly higher than those in the equivalent (001) lasers.

Valence subband structures of (101̄0)-GaN/AlGaN strained quantum wells calculated by the tight-binding method

The effect of biaxial strain on the valence bands in (1010)-GaN/AlGaN quantum wells (QWs) is theoretically investigated, using the sp3 tight-binding method. The effective mass around the valence band edge in unstrained (1010) QWs is reduced to about 1/2 that of (0001) QWs. Under compressive strain, the subband non-parabolicity near the band edge is further reduced due to heavy-hole/light-hole splitting. The optical matrix elements of [1120] polarization in these QWs are twice as large as those in (0001) QWs. The reduced effective mass and large optical matrix elements in the (1010) QWs are an advantage for short-wavelength laser diodes based on wurtzite GaN.

Orientation dependence of optical properties in long wavelength strained quantum-well lasers

The dependence of optical properties on crystal orientation is analyzed for long wavelength strained quantum-well (QW) GaAsP-InGaAsP lasers. The calculation is based on the multiband effective mass theory which enables us to consider the anisotropy and the nonparabolicity of the valence-band dispersions. It is found that the optical gain increases as the crystal orientation is inclined from [001] toward [110]. This is due to the reduced valence-band density of states. The differential gain is about 1.6 times larger for the [110]-oriented 1.55-/spl mu/m strained QWs than for equivalent [001]-oriented QWs. It is also shown that the threshold current density in 1.3-/spl mu/m strained QW lasers decreases to two-thirds of that in the [001]-oriented laser as the orientation is inclined away from [001] by 40/spl deg/-90. >

Dependence of optical gain on crystal orientation in wurtzite–GaN strained quantum-well lasers

Optical gains in wurtzite–GaN strained quantum-well (QW) lasers are estimated theoretically for various crystallographic directions. The calculation of the valence subbands is based on the k⋅p theory, where deformation potentials are determined by a semiempirical tight-binding method. It is found that the gains in GaN strained QW lasers with non-(0001) orientations, particularly around the (1015) orientation, are markedly high and anisotropic, unlike those in (0001)-oriented lasers.

Spiral growth of InGaN/InGaN quantum wells due to Si doping in the barrier layers

We have examined Si-doping effects in InGaN/InGaN quantum-well (QW) structures, especially the influence of Si-doped InGaN barrier layers on the growth mechanism of QW structures, by atomic force microscopy (AFM) and by photoluminescence (PL) and cathodoluminescence (CL) spectroscopy. Our AFM observations revealed that Si-doped InGaN barriers strongly affect the growth mode of overlying InGaN QW layers. This effect leads to the formation of nanoscale islands (with a density of 108 cm−2) due to spiral growth of the QW layers. The spirally grown nanoscale islands significantly increase the PL intensity. Through spatially resolved CL observations, we found that the number of dot-like CL bright spots increased dramatically when the barrier layers were Si doped, and the increased density of the spots was in good agreement with the increased density of the nanoscale islands observed by AFM. By combining these results, we show that the spirally grown QW structures produced by Si doping of the barriers effectivel...

GaNAs grown by gas source molecular beam epitaxy

Abstract The two main keys to growing GaNAs are reducing layer thickness and using a highly efficient N source. Through careful and precise growth control, GaNAs is grown with a N content of up to about 10% by gas source molecular beam epitaxy in which a N radical is used as the N source.

Optical Properties of GaN Thin Films on Sapphire Substrates Characterized by Variable-Angle Spectroscopic Ellipsometry.

The optical properties of GaN thin films grown on sapphire substrates by low-pressure metal organic chemical vapor deposition were investigated by variable-angle spectroscopic ellipsometry. Accurate refractive indices (n, k) below, through, and above the fundamental bandgap of GaN in the spectra range of 1.5 to 3.8 eV (330 to 830 nm) were determined by using a parametric semiconductor model that took the surface roughness effect into account. The fundamental bandgap energy (3.41 eV) of GaN determined by the model was exactly the same as that obtained from an optical transmission experiment using the same sample. The high-frequency dielectric constant e∞ (=5.2) of GaN for (E⊥c) obtained from the ellipsometric measurement was also in excellent agreement with the experimental value of 5.2±0.1 (E⊥c) from the IR reflectivity measurements.

Crystal Orientation Effect on Valence-Subband Structures in Wurtzite-GaN Strained Quantum Wells

We analyze theoretically for the first time valence-subband structures in wurtzite-GaN strained quantum wells (QWs) for various crystal orientations. The calculation is based on the Bir-Pikus effective-mass theory, where deformation potentials are determined by a semi-empirical tight-binding method. The obtained results show that the hole effective masses of strained QWs with non-(0001) orientation, in particular, around the (10*BAR*1*BAR*2) orientation, are markedly lighter than those of (0001) cases. We also found that the optical matrix elements of non-(0001) strained QWs are twice as large as those for (0001) strained QWs.

Tight-Binding Analysis of the Optical Matrix Element in Wurtzite- and Zincblende-GaN Quantum Wells

The polarization dependence of the optical matrix element in wurtzite- and zincblende-GaN quantum wells (QWs) is theoretically investigated, based on the sp3 tight-binding model which takes into account the spin-orbit interaction and crystal field splitting. The optical matrix element in wurtzite-GaN QWs has no dependence on the wave number due to its anisotropy along the c axis. We also show that the optical matrix element for the conduction-light hole transition in wurtzite-GaN QWs is about three times larger than that for bulk zincblende GaN. These results suggest that wurtzite GaN will be useful for light emitting devices due to its apparent high optical transition.