S. Sugou

Ground-state lasing at room temperature in long-wavelength InAs quantum-dot lasers on InP(311)B substrates

InAs quantum dots (QDs) with a high density of 9×1010 cm−2 are formed on InAlGaAs layer/InP (311)B substrates. Lasers having five-period stacked InAs QD layers are operated in the ground state (λ≈1.6 μm) at room temperature, and the maximal modal gain of the ground state is measured to be 20 cm−1. We obtained a threshold current density of 380 A/cm2 at room temperature, and observed the temperature-insensitive threshold current at temperatures from 77 to 220 K.

Critical layer thickness on (111)B‐oriented InGaAs/GaAs heteroepitaxy

The critical layer thickness of lattice‐mismatched InGaAs on (111)B‐oriented GaAs was investigated by monitoring surface lattice relaxation using streak spacing on the reflection high‐energy electron diffraction pattern. The critical layer thickness (hc) grown on (111)B was about twice that of a (100) under the same growth conditions. A qualitative explanation for the enhancement of hc is given based on the mechanical equilibrium theory developed by J. W. Matthews and A. E. Blakeslee [J. Cryst. Growth 27, 118 (1974)] for a strained single heterostructure.

Analysis of leakage current in buried heterostructure lasers with semiinsulating blocking layers

An effective device structure for reducing leakage current in buried heterostructure laser diodes with semi-insulating InP blocking layers is analyzed. The analysis utilizes a semiconductor device simulator in which deep trap levels are taken into account. It predicts that the addition of a thin wide-bandgap InGaP layer in the semi-insulating region at the mesa boundaries as a barrier to prevent double injection into the semi-insulating region is effective in reducing leakage current. >

Semi-insulating current blocking property simulations for buried heterostructure laser diodes

A compound‐semiconductor device simulator, in which deep levels in the semi‐insulating layers can be taken into account, has been developed. By using this simulator, the electrical properties for the semi‐insulating InP buried heterostructure laser diodes were investigated. The leakage current, without passing through the active region, was found to be small when the trap density in the semi‐insulating InP layers is more than 3×1015 cm−3 and less than 1×1016 cm−3. This simulator will be a useful tool in predicting the semi‐insulating properties of electrical and optical semiconductor devices.

Low-threshold lasing at 1.3 /spl mu/m from GaAsSb quantum wells directly grown on GaAs substrates

Material systems on GaAs that can emit at 1.3 /spl mu/m have been attracting great interest from the viewpoint of realizing long-wavelength vertical-cavity surface-emitting lasers (VCSELs) that use high-reflectivity GaAs-AlAs distributed Bragg reflectors (DBRs). We previously investigated GaAsSb quantum-well (QW) layers on GaAs. By improving the GaAsSb optical quality and optimizing the laser structure, we have since achieved low-threshold lasing at a longer wavelength of 1.27 /spl mu/m in the GaAsSb-GaAs material system.

High-quality 1.3-/spl mu/m AlGaInAs MQW growth on a grating and its application to BH DFB-LDs for uncooled 10-Gb/s operation

A process for growing a high-quality AlGaInAs MQW on a grating has been developed and applied to fabricate a 1.3-/spl mu/m AlGaInAs BH DFB-LD. A low threshold current of 20 mA, a high slope efficiency of 0.31 W/A at 85/spl deg/C and a high CW operating temperature of 120/spl deg/C were obtained for a 250-/spl mu/m-long device with antireflective and high-reflective coated facets. A clear eye opening under 10-Gb/s direct modulation was also confirmed at 85/spl deg/C.

GaAsSb/GaAs 1.3-/spl mu/m-VCSELs for 10 G-bit Ethernet

We demonstrated high-performance GaAsSb VCSELs emitting at 1.295 /spl mu/m with a low threshold current of 1.1 mA and a maximum cw operating temperature of 70 C. After the high-frequency modulation characteristics have been validated, the GaAsSb VCSELs should be viable low-cost light sources for high bandwidth fiber communications.

High-performance 1.3-/spl mu/m VCSELs with GaAsSb/GaAs quantum wells

We have demonstrated CW and high-speed performance of GaAsSb/GaAs VCSELs lasing at a wavelength of longer than 1.27 /spl mu/m. 1.295 /spl mu/m lasing was achieved with a threshold of 1.1 mA. Single-mode output of 0.46 mW, and 4.5-GHz bandwidth was obtained at 1.27 /spl mu/m. Thus, GaAsSb/GaAs VCSELs should be viable low-cost light sources for high-capacity optical fiber systems.

Continuous-wave operation of 1.27-/spl mu/m GaAsSb/GaAs VCSELs

1.27-/spl mu/m VCSELs using GaAsSb quantum wells, which operate continuous-wave at and above room temperature (RT), are reported. A threshold current as low as 0.7 mA at RT and a maximum cw operating temperature of 70/spl deg/C are demonstrated. This result was achieved by optimizing the active-layer structure with respect to strain. Thus, GaAsSb VCSELs are viable low-cost light sources for high-bandwidth fiber communications.

GaAsSb-based alloys for long-wavelength lasers

We will review the growth, structural, and optical properties of GaAsSb QWs and the material gain improvement of lasers using modulation doping in the active region and the state-of-the-art device performance of GaAsSb VCSELs. We grew GaAsSb QWs with GaAs barriers on n-GaAs [100] substrates by using gas-source molecular beam epitaxy (GSMBE) and metal-organic vapor phase epitaxy (MOVPE).