Masao Kawaguchi

Lasing Characteristics of Low-Threshold GaInNAs Lasers Grown by Metalorganic Chemical Vapor Deposition

We report on the lasing characteristics of low-threshold long-wavelength GaInNAs double quantum well (DQW) lasers grown by metalorganic chemical vapor deposition (MOCVD). We have achieved a threshold current density of 450 A/cm2 for a 1.28-µm-emitting laser. This is the lowest value for 1.3-µm-range GaInNAs lasers grown by MOCVD. We also observed high characteristic temperatures (T0) of 210 K and 130 K for 1.25 µm and 1.28 µm lasers, respectively. In addition, we investigated the gradual change in lasing characteristics under pulsed operation. The blue shift of an emission wavelength and a threshold current reduction were observed, which is similar to that observed in the thermal annealing of GaInNAs.

Lasing Characteristics of 1.2 µm Highly Strained GaInAs/GaAs Quantum Well Lasers

In this study, we demonstrate a highly strained 1.2 µm GaInAs/GaAs quantum well laser which may be used in high-speed local area networks. Edge emitting lasers with either a GaInP or AlGaAs cladding layer have been fabricated. We have achieved a threshold current density as low as 170 A/cm2 for GaInP-cladding-layer lasers and a high characteristic temperature T0 as high as 211 K from 30°C to 120°C for AlGaAs-cladding-layer lasers. The material gain coefficient g0 was estimated to be 1550 cm-1 which is comparable to that of 0.98 µm GaInAs lasers. A preliminary lifetime test under heatsink-free CW condition was carried out, which shows no notable degradation after 300 h. We also demonstrated an AlAs oxide confinement laser in a 1.2 µm wavelength band.

Critical layer thickness of 1.2-μm highly strained GaInAs/GaAs quantum wells

In this paper we experimentally determined the critical layer thickness for highly strained 1.2-μm GaInAs/GaAs quantum wells of good crystal quality. The dependence of the critical layer thickness on the indium content indicates that the observed quality degradation is caused by a growth mode transition. This is also supported by transmission electron microscopy measurements. We discuss the possibility of extending the wavelength of highly strained GaInAs/GaAs quantum wells toward 1.3 μm by delaying the growth mode transition. As a first step, a wavelength extension to 1.225 μm is achieved by using the presented technique.

Inclusion of Strain Effect in Miscibility Gap Calculations for III–V Semiconductors

A new and simple treatment of miscibility gap calculations for ternary and quaternary semiconductors including strain is presented. Our treatment leads to the same result as that of previous treatments, in the case of lattice-matched layers, but provides a more realistic and rigorous description for coherently strained layers. We also discuss the differences between our treatment and previous treatments, including misfit strain caused by the substrate. Our treatment is applied in miscibility gap calculations for GaInNAs and GaInAsSb material systems. Theoretical predictions by miscibility gap calculations are compared with growth experiments and show reasonable agreement.

GaInAs-GaInNAs-GaInAs intermediate layer structure for long wavelength lasers

Proposes two new structures, the GaInAs-GaInNAs intermediate layer (IML) and the GaInN/sub x/As graded wells, which show better optical properties than the commonly used GaInNAs-GaAs rectangular quantum-wells. A 1240-nm emitting IML laser has been achieved with a low-threshold current density (200 A/cm/sup 2//well) and a relatively high characteristic temperature (T/sub o/=100 K). The IML structure is very promising for long wavelength GaAs-based laser applications.

Optical Quality Dependence on Growth Rate for Metalorganic Chemical Vapor Deposition Grown GaInNAs/GaAs

GaInNAs/GaAs quantum wells with indium compositions of up to 39% were grown by metalorganic chemical vapor deposition under different growth rates. We found that the growth rate (~1 µm/h) critically affects the optical quality of GaInNAs/GaAs quantum wells and that a low growth rate (~0.2 µm/h) is preferable for increasing nitrogen compositions.

Photoluminescence dependence on heterointerface for metalorganic chemical vapor deposition grown GaInNAs/GaAs quantum wells

We investigate the effect of the sequence of gas flows at heterointerfaces on optical quality of GaInNAs/GaAs quantum wells grown by metalorganic chemical vapor deposition (MOCVD). We point out that the degradation mechanism of photoluminescence of GaInNAs grown by MOCVD method is categorized in two types. One is the formation of a GaNAs layer at the heterointerface which causes both increase of emission wavelength and degradation of crystal quality. The other is generation of nonradiative centers induced by incorporation of nitrogen (N). The insertion of a GaInAs layer to the GaInNAs/GaAs heterointerface is proposed to overcome these degradation mechanisms. A GaInAs intermediate layer is effective to suppress the GaNAs formation and to reduce the total GaInNAs thickness.

High Temperature Characteristics of Nearly 1.2 µm GaInAs/GaAs/AlGaAs Lasers

We have demonstrated a highly strained GaInAs/GaAs double quantum well laser operating at nearly 1.2 µm with AlGaAs cladding layers for the first time. Our previously reported high characteristic temperature of 150 K was improved to 202 K for a 410-µm-long broad-area GaInAs/GaAs/AlGaAs laser in the temperature range from 30°C to 70°C. The threshold current density of this laser was as low as 370 A/cm2.

Improvement in Photoluminescence Efficiency of GaInNAs/GaAs Quantum Wells Grown by Metalorganic Chemical Vapor Deposition for Low-Threshold 1.3 µm Range Lasers

A quality improvement of the III–V dilute nitride semiconductor alloy, GaInNAs, grown by metalorganic chemical vapor deposition (MOCVD) on a GaAs substrate is reported for 1.3 µm-wavelength lasers. GaInNAs wafers were grown at various growth temperatures, V/III ratios, and growth rates. The photoluminescence (PL) efficiency of GaInNAs/GaAs quantum wells (QWs) was increased by lowering the growth temperature and increasing the V/III ratio in the growth conditions conventionally used for nitrogen (N)-free GaInAs/GaAs QW growth. These conditions are important for realizing high PL efficiency because they prevent the inhomogeneity of the immiscible alloy of GaInNAs. It was also observed that the optimal window for the growth temperature, V/III ratio, and growth rate for the GaInNAs is narrower than that of N-free GaInAs QWs. After careful optimization of the growth conditions, GaInNAs/GaAs QW lasers with various emission wavelengths were fabricated. Low-threshold current densities of 0.17 kA/cm2/well, 0.18 kA/cm2/well, and 0.44 kA/cm2/well are obtained for emission wavelengths of 1.25 µm, 1.30 µm, and 1.34 µm, respectively. The results obtained for growth conditions and lasing characteristics are useful in further improving 1.3 µm or longer wavelength GaInNAs lasers grown by MOCVD.

Photoluminescence and Lasing Characteristics of GaInNAs Quantum Wells Using GaInAs Intermediate Layers

We have studied photoluminescence (PL) properties of GaInNAs quantum wells (QWs) which have GaInAs intermediate layers (IML) inserted at the GaInNAs/GaAs heterointerfaces. Lasing characteristics of the laser using IML are also investigated. We point out that the total amount of nitrogen (N) in the GaInNAs QW could be reduced by using the GaInAs IML while maintaining the emission wavelength. We also found that the optical quality of the GaInNAs IML QWs depends on both the N composition and the total amount of N incorporated in the QW. Due to the reduced total amount of N, an IML QW evidently exhibited a better PL property than a conventional rectangular potential QW. No deterioration in lasing characteristics was observed for GaInNAs lasers using GaInAs IML. The GaInAs IML structure with an appropriate design is expected to lead to improved lasing characteristics of GaInNAs lasers.