Takeo Kageyama

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.

High-temperature operation up to 170/spl deg/C of GaInNAs-GaAs quantum-well lasers grown by chemical beam epitaxy

High-temperature pulsed operation of GaInNAs-GaAs double-quantum-well lasers grown by chemical beam epitaxy has been demonstrated for the first time. The lasing wavelength was from 1.20 to 1.27 /spl mu/m with different composition at room temperature. The highest lasing operation temperature up to 170/spl deg/C and a high characteristic temperature of 270 K were obtained for 300-/spl mu/m-long lasers at 1.2 /spl mu/m.

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.

Sb surfactant effect on GaInAs/GaAs highly strained quantum well lasers emitting at 1200 nm range grown by molecular beam epitaxy

A surfactant effect of antimony (Sb) on highly strained GaInAs quantum wells (QWs) was studied by molecular beam epitaxy. Noticeable improvement of the photoluminescence (PL) was observed by adding the dilute Sb. The QWs showed an increased PL intensity and narrow linewidth of 23 meV for the wavelength range up to 1180 nm. An atomic force microscope study showed a flattened surface morphology by the introduction of the Sb. Broad-area lasers with a GaInAsSb/GaAs double-QW active layer emitting at 1170 nm showed a low threshold current density of 125 A/cm2 per well for an infinite cavity length.

Surfactant effect of Sb on GaInAs quantum dots grown by molecular beam epitaxy

A surfactant effect of antimony (Sb) was investigated for self-assembled GaInAs quantum dots (QDs). The introduction of Sb into the QDs cause a large blue shift of the photoluminescence (PL) wavelength with a decrease in the full width at half maximum (FWHM) and an increase in intensity in comparison with QDs without Sb. Atomic force microscope (AFM) measurement showed a marked reduction in QD density from 1.0×1010 cm-2 to 7.0×107 cm-2. This indicates that Sb suppresses the formation of QDs and that the wetting layer remains to be a quantum well (QW) structure. The PL wavelength of the GaInAsSb wetting layer was elongated by increasing the amount of Sb supply. This result indicates the expansion of the critical thickness of the growth mode change from 2D to 3D.

GaInNAs/GaAs Quantum Well Growth by Chemical Beam Epitaxy

This is the first report on chemical beam epitaxy (CBE) of GaInNAs/GaAs quantum wells (QWs). From the observed clear X-ray diffraction satellite peaks, the QW structure incorporating nitrogen supplied by radical nitrogen was successfully grown. The photoluminescence emission with the emission peak wavelength of 1.0 µm was observed from GaInNAs/GaAs QWs at room temperature. The wavelength could be elongated by increasing the amount of nitrogen and indium.

Chemical Beam Epitaxy Growth and Characterization of GaNAs/GaAs

A GaNAs layer has been grown on a GaAs substrate using chemical beam epitaxy (CBE) with a radio frequency (RF) radical nitrogen source for the first time. The nitrogen (N) composition was well-controlled by the N2 flow rate and was increased up to 2.7%, maintaining a good crystal quality. The maximum N composition was estimated to be 20% by a secondary ion mass spectroscopy (SIMS) measurement. The N composition estimated from both X-ray diffraction measurements and SIMS measurements were in good agreement. This shows that the N composition can simply be determined by X-ray diffraction measurements. The optical absorption measurement of the grown GaNAs was also carried out. The bandgap bowing parameter of GaNAs was found to be not a constant and varied between 15–23 eV for N<2.7%. An empirical expression of bandgap vs. composition was obtained for a N composition below 3%.

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.

Extremely high temperature (220°C) continuous-wave operation of 1300-nm-range quantum-dot lasers

High temperature (>125°C) resistant semiconductor lasers are attractive as light sources in a variety of harsh environments [1]. Long-wavelength lasers operating under higher temperature of more than 200°C combined with silica-based optical fibers can expand application fields of data transmission and optical sensing to severe environments like space or deep underground. Temperature dependence of the threshold current of a semiconductor laser can be drastically reduced by employing quantum-dot (QD) active layers [2, 3]. Recent progress in epitaxial growth technology of QDs enhances the laser characteristics [3, 4]. Here, we report extremely high temperature continuous-wave (CW) operation up to 220°C of QD lasers emitted at 1300-nm-range for the first time by enhancing gain and increasing the quantized-energy separation of the QD active layers. Thus, QD lasers are proved to be suitable light sources for high temperature resistant applications.