Takao Kuroda

Channeled‐substrate planar structure (AlGa)As injection lasers

Undesirable nonlinear ’’kinks’’ in light‐output–vs–current characteristics of stripe geometry double‐heterostructure (DH) injection lasers are significantly reduced by stabilizing the transverse modes along the junction plane. Built‐in passive guiding mechanism is introduced by growing planar (AlGa)As/GaAs DH layers on a grooved GaAs substrate.

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.

Monolithic integration of a GaAlAs injection laser with a Schottky‐gate field effect transistor

Monolithic integration of a GaAlAs laser with a GaAs Schottky‐gate field effect transistor is demonstrated. A GaAs field effect transistor with a 3‐μm gate length is formed on a double‐heterostructure laser crystal which is protected by a high‐resistivity isolation layer. Laser light intensity is modulated to realize rise and fall times of less than 0.4 ns by modulating the field effect transistor gate voltage.

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.

Transverse-mode stabilized Ga 1− xAlxAs visible diode lasers

Transverse-mode stabilized visible diode lasers in the 0.7-microm wavelength region are fabricated by growing a Ga(1-x)Al(x)As double heterostructure on a grooved GaAs substrate (channeled-substrate-planar structure). The diodes operate stably in the fundamental transverse mode and provide nonstigmatic laser beams. They can be collimated with a 0.5-1-mrad beam divergence using a simple graded-index fiber lens. Corresponding to single-longitudinal-mode operation at current levels above 1.1 times the threshold, a coherence length as long as 14 m is obtained in Michelson interference experiments.

Channeled-substrate-planar structure AlxGa 1− x As lasers: an analytical waveguide study

The waveguide mechanism in channeled-substrate-planar (CSP) structure (AlGa) As lasers is analyzed. The light leakage into the GaAs substrate outside the channel is shown to provide effective refractive index and loss differences, which function to stabilize the transverse mode in the junction plane. Observed light output vs current characteristics and mode patterns in the lasers justify the theoretical model.

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.

Channeled‐substrate‐planar structure distributed‐feedback semiconductor lasers

Distributed‐feedback Ga1−xAlxAs lasers with a channeled‐substrate‐planar structure are fabricated. They operate in single transverse and longitudinal modes. No spectral broadening or excess noise is observed under high‐frequency modulation as a result of mode stabilization.