Michinori Irikawa

Carrier confinement by multiple quantum barriers in 1.55 μm strained GaInAs/AlGaInAs quantum well lasers

Carrier confinement performance by multiple quantum barriers (MQB) is demonstrated in 1.55 μm strained GaInAs/AlGaInAs multiple quantum well (MQW) lasers grown by molecular beam epitaxy. The strained MQW lasers with MQB at p‐side optical confinement layer show larger characteristic temperature and slope efficiency at high temperature than those without MQB. It is also shown that the MQW lasers with MQB have less spontaneous emission from the optical confinement layer than the lasers without MQB. As another important result, it is demonstrated for the first time that the MQW lasers with MQB have less dependency of the K factor on the temperature than the lasers without MQB. These results further verify the effective carrier confinement performance of GaInAs/AlInAs MQB structure.

Improved Theory for Carrier Leakage and Diffusion in Multiquantum-well Semiconductor Lasers.

A model of carrier leakage lifetime is presented taking into account the density of states for quantum-wells and band nonparabolicity. Rate equations are also proposed including leakage of both types of carriers and carrier loss in both sides of optical confinement layers. The carrier loss coefficients extracted by adopting this model on the measured modulation bandwidth of 1.5 µm-wavelength multiquantum-well lasers coincided with reported values within their distributions. Measured temperature sensitivity of threshold current and that of K factor were also well explained with the improved model using those extracted carrier loss coefficients. The dominant causes of low characteristic temperature T0 of present compressive-strained multiquantum-well lasers were quantitatively considered and found to be attributed to 1) Auger carrier loss and 2) thermionic carrier leakage and diffusion delay effect. T0 over 150 K is expected by reducing the effect of those two factors. Possibilities of finding an actual method to reduce the effect of the above two factors are discussed.

Some effects of conduction band nonparabolicity on electron reflection spectrum of multiquantum barriers

The effect of nonparabolicity of conduction band on the electron reflection spectrum of multiquantum barriers (MQB) has been examined. Drastic reduction in the effective barrier height is expected by adopting the nonparabolic model on the MQB which had been designed using the parabolic model for 1.5 μm semiconductor lasers (LDs). The predicted enhancement in barrier height by the MQB is over 600 meV under parabolic model. However, it decreases to 40 meV under nonparabolic model with the same structure. On the other hand, the experimental enhancement in barrier height by the MQB is estimated to be around 30 meV on 1.5 μm LDs, close to the value calculated by nonparabolic model. Those results suggest that a much higher effective barrier height can be realized by optimizing the MQB design taking the nonparabolicity into account. The conduction band nonparabolicity was incorporated by the k⋅p perturbation method.

Strained-Layer Multi-Quantum Barriers for Reducing Hot Electron Leakage in Long-Wavelength Semiconductor Lasers

Multi-quantum barriers with a 1%-tensile-strained AlInAs/GaInAsP system are proposed for the purpose of suppressing the overflow leakage of hot electrons generated by the Auger effect. It is theoretically demonstrated for the first time that an effective barrier height of 1.2 eV, which is sufficient to confine hot electrons, can be obtained for 1.3 µm GaInAsP lasers. This implies that the overflow is almost suppressed, and dramatic improvement of high-temperature operation is expected.

New fabrication method for 1.3‐μm GaInAsP/InP buried crescent lasers using a reactive ion beam etching technique

A 1.3‐μm GaInAsP/InP buried crescent laser on a p‐type InP substrate was demonstrated. An active region width narrower than 1.5 μm was achieved with good controllability and reproducibility using the newly introduced reactive ion beam etching technique for the etching process. Stable fundamental transverse mode operation with low threshold currents of 15–25 mA was obtained. Less than 5% degradation in threshold current at 50 °C was achieved with a constant driving current of 150 mA at 70 °C for 100 h.

Strained Layer Multiquantum Barriers with Improved Carrier Injection and Confinement.

The effects of using strained layer superlattice in multiquantum barriers (MQBs) were analyzed with focus on InP-based materials and their application to strained layer multiquantum well lasers (SL-MQW LDs). Tensile strained barriers are shown to largely increase the effective barrier height of MQBs. A new barrier material, AlInP, which is 1–1.5% tensile strained on InP, is shown to have inherent advantages of large conduction band edge discontinuity ΔEc and low aluminum content compared to conventional AlInAs on InP. Those advantages are confirmed for strain-compensated MQB with tensile barrier/compressive well in terms of increasing the effective barrier height. Some disadvantages of the strain-compensated MQB are also pointed out; the increase in density of holes injected into the MQB region under lasing conditions and the high p-doping concentration required. To solve those problems, an improved method of carrier injection through minibands with gradually enhanced energy levels toward the MQW region is presented, which is shown to enable elimination of the carrier transport effect and to result in marked improvement in laser performances.

Low dark current AlGaInAsInP waveguide photodiodes using hybrid MBE and MOCVD growth

Abstract Dark current of 7pA with one cleaved facet and 20pA with an anti-reflection coating at the reverse bias voltage of 3 V was obtained for AlGaInAs InP pin waveguide photodiodes, in which an AlGaInAs absorption layer and optical confinement layers were grown by optimized molecular beam epitaxy and an upper InP cladding layer was grown by metal-organic chemical vapor deposition. This is the lowest known dark current reported for long-wavelength pin waveguide photodiodes to date.

Molecular-beam-epitaxy growth of strained Ga1−x InxAs/AlInAs/InP and application to 1.55 μm multi-quantum-well lasers

Abstract Dependence of critical layer thickness ( h c ) and photoluminescence (PL) intensity on growth temperature ( T g ) was investigated for 1% compressively strained Ga 0.32 In 0.68 As/AlInAs on InP. We found, for the first time, a strong T g dependence of h c in this system with h c of 24 nm at 500°C and 14 nm at 530°C. The PL intensity increased with T g , reaching a maximum at 530°C. We fabricated 1.55 μm multi-quantum-well (MQW) lasers with 1% compressively strained wells under optimized growth conditions. Threshold current density as low as 1.08 kA/cm 2 at a cavity length of 800 μm was obtained. This threshold current density is one of the lowest values obtained for 1.55 μm AlGaInAs MQW lasers grown by molecular beam epitaxy (MBE).

1.55 μm InGaAs/InAlAs/InP Quantum Wells with Mass-Dependent Width for Polarization-Independent Optical Modulation

We describe a new quantum well structure in 1.55 µ m materials where the effective width of the well is mass-dependent. This is advantageous for polarization-independent modulation of 1.55 µ m optical waves. An InGaAs/InAlAs multiple quantum well p-i-n diode with such a structure on an InP substrate has been fabricated for the first time, and its photocurrent spectra have been measured. We have observed a larger Stark shift for light-hole exciton than that for heavy-hole exciton, which never occurred in conventional quantum wells. Therefore, the same amount of Stark shift for both holes should be possible by adjusting such a quantum well structure with mass-dependent width.

1.5 μm wavelength compressively strained GaInAs/AlGaInAs multiquantum‐well lasers grown by molecular‐beam epitaxy with high differential gain and low threshold current density

1.5 μm GaInAs/AlGaInAs multiquantum‐well (MQW) lasers with 1% compressively strained quantum wells were grown by molecular‐beam epitaxy. The effective differential gain (g0) determined from the squared relaxation oscillation frequency versus output power relations is a high value of 9.3×10−16 cm2 in long‐wavelength lasers. On the other hand, the effective transparent carrier density (n0) of strained‐layer MQW lasers determined from the measurement of the spontaneous carrier lifetime was found to be very high, which is different from the theory of strain effects. However, by taking the carrier transport effect into account, it was shown that (1) for the strained MQW lasers the intrinsic transparent carrier density is lower than that of the lattice‐matched MQW lasers, and (2) the intrinsic value of g0 is estimated to be 28–56×10−16 cm2, which is close to the theoretically predicted value. By improving the laser structure to have better carrier transport, much higher effective differential gain and lower eff...