Shigeki Makino

Thermal Annealing of GaInNAs/GaAs Quantum Wells Grown by Chemical Beam Epitaxy and Its Effect on Photoluminescence

The thermal annealing effect on the photoluminescence (PL) characteristics of GaInNAs/GaAs quantum wells (QWs) grown by chemical beam epitaxy (CBE) using radical nitrogen is presented. The room-temperature PL peak intensity of GaInNAs/GaAs QWs increased about 70 times and the linewidth of PL spectra decreased after annealing at 675°C for 30 seconds. The blue shift of the PL peak wavelength of GaInNAs/GaAs QWs and GaNAs/GaAs QWs, due to the structural change of QWs was observed. It was found that the blue shift was caused by In–Ga interdiffusion rather than nitrogen atom diffusion. The interdiffusion caused by defects is thought to reduce the number of non radiative centers, resulting in the improvement of PL characteristics. The optimum annealing temperature depends on the composition.

CBE and MOCVD growth of GaInNAs

We have investigated growth of GaInNAs by MOCVD using dimethylhydrazine (DMHy) and by CBE using RF-radical nitrogen. It was found that there was a large difference in nitrogen incorporation characteristics between the two growth methods. Nitrogen composition of MOCVD increased with a superlinear characteristic against nitrogen source flow and indium composition enhanced such a characteristic. CBE showed a linear incorporation characteristic of nitrogen composition due to the strong reactivity of nitrogen atoms. Photoluminescence intensity was decreased by increasing emission wavelength for both growth techniques, however, the degradation behavior seemed to depend on the nitrogen incorporation characteristic. The hydrogen and carbon concentration of MOCVD grown sample was more than ten times larger than that of CBE grown samples. The comparison of growth characteristics and material qualities may provide useful information for improving the GaInNAs crystal quality.

Optical quality of GaNAs and GaInNAs and its dependence on RF cell condition in chemical beam epitaxy

Optical quality of GaNAs and GaInNAs quantum wells and its dependence on RF radical cell operation in chemical beam epitaxy (CBE) were investigated. It was shown that nitrogen atoms are main plasma species responsible for the CBE growth of GaNAs and related alloy. By choosing aperture flow conductance, significant improvement in photoluminescence of GaInNAs/GaAs quantum well at 1.2 μm wavelength region have been demonstrated. The reduction of ions are found to be effective to improve crystal quality.

p-Type Doping Characteristics of GaInNAs:Be Grown by Solid Source Molecular Beam Epitaxy

We investigated the doping and electrical characteristics of p-type GaInNAs for use in a p-contact layer and in the p-distributed Bragg reflectors ( p-DBRs) of surface emitting lasers. Beryllium doping was applied to GaInNAs grown by solid source molecular beam epitaxy with the nitrogen radical. The doping efficiency for the lattice-matched GaInNAs is similar to that of the GaAs, and a slight deterioration in hole mobility indicates the alloy scattering of the GaInNAs.

1.4 µm GaInNAs/GaAs Quantum Well Laser Grown by Chemical Beam Epitaxy

We have achieved room-temperature pulsed operation of 1.4-µm-wavelength GaInNAs/GaAs double quantum well (DQW) lasers with increased nitrogen composition up to 1.7% grown by chemical beam epitaxy (CBE). A threshold current density of 8.9 kA/cm2 was obtained, and the characteristic temperature (T0) from 10 to 40°C was 94 K.

Nitrogen Composition and Growth Temperature Dependence of Growth Characteristics for Self-Assembled GaInNAs/GaAs Quantum Dots by Chemical Beam Epitaxy

A GaInNAs/GaAs quantum dot (QD) system is anticipated as a novel material to extend the emission wavelength of GaAs-based lasers. We have studied GaInNAs QDs by chemical beam epitaxy (CBE). The growth temperature and nitrogen composition dependence on the size and density of GaInNAs QDs were investigated. The growth characteristics of GaInNAs QDs were quite different from those of GaInAs QDs. It was found that the GaInNAs QDs showed a small change in size and the density through the temperature range from 500°C to 540°C, although the size increased and the density decreased for GaInAs QDs with increasing growth temperature. The density of about 9×1010 cm-2 was obtained for GaInNAs QDs at 540°C. This value is three times larger than that of GaInAs QDs grown at 530°C. These results indicate a marked change in the migration length of adatoms due to the nitrogen introduction. The nitrogen introduction effect on QD formation may be advantageous for improving the gain characteristics of long-wavelength QD lasers.

Composition Dependence of Thermal Annealing Effect on 1.3 µm GaInNAs/GaAs Quantum Well Lasers Grown by Chemical Beam Epitaxy

The thermal annealing process is effective to improve the optical quality of GaInNAs/GaAs quantum wells (QWs). However, a blue shift of the emission peak wavelength occurs during the annealing and it is strongly related to the annealing condition and the composition of GaInNAs/GaAs QWs. In this study, we investigated the dependences of both the annealing condition and the composition on the lasing characteristics of 1.3 µm GaInNAs/GaAs QW lasers.

CBE growth of GaInNAs quantum wells and dots for long-wavelength lasers

The GaInNAs is an attractive material for long wavelength lasers on a GaAs substrate and the GaInNAs vertical cavity surface emitting laser (VCSEL) is a viable candidate for low cost and high performance lasers of 1.3micrometers wavelength networks due to excellent temperature characteristics and manufacturing capability of VCSELs. We have successfully grown GaInNAs quantum wells by chemical beam epitaxy and investigated the growth condition toward better crystal quality by employing a radical nitrogen source and thermla annealing. Lasing characteristics of CBE grown 1.2 micrometers GaInNAs lasers are a threshold current density of less than 1kA/cm2, and high temperature operation up to 170 degrees C with an excellent slope efficiency change below -0.004dB/K. A characteristic temperature of 270K is also demonstrated. GaInNAs quantum dots were also investigated for the further progress of GaInNAs lasers. The growth of self-organized Qds and a lasing operation at 77K was demonstrated.

Investigation of well thickness reduction effect of GaInNAs/GaAs quantum well lasers

We investigated the advantageous of a thin quantum well (QW) for GaInNAs laser performances. We pointed out that the reduction of the well thickness has almost no disadvantage on the optical gain and the carrier overflow due to a large conduction band offset. A thin QW is advantageous for suppression of the carrier overflow to the higher quantized energy levels which results In good temperature and gain characteristics. A thin GaInNAs QW is a good candidate for an active layer structure of the laser utilized in high performance optical communication systems.

Thermal annealing effect on self-assembled GaInNAs/GaAs quantum dots grown by chemical beam epitaxy

The self-assembled GaInNAs quantum dot (QD) has proposed as a novel material system for long wavelength lasers on GaAs substrate. In this paper, we have investigated the thermal annealing effect on GaInNAs QDs. The increase of the PL intensity and blue shift of peak wavelength was observed by thermal annealing. For 600/spl deg/C annealing, the PL intensity was increased with the increase of annealing time and maximum intensity was obtained at 2 hours. On the other hand, PL intensity was increased after 30s annealing, then decreased at longer time for 700/spl deg/C annealing. A larger blue shift of peak wavelength compared to GaInNAs quantum well was observed. It is considered that the interdiffusion was enhanced in QD system due to its large strain and interface area between GaAs capping layer.