Masahiko Kondow

GaInNAs: a novel material for long-wavelength semiconductor lasers

GaInNAs was proposed and created in 1995 by the authors. It can be grown pseudomorphically on a GaAs substrate and is a light-emitting material having a bandgap energy suitable for long-wavelength laser diodes (1.3-1.55 /spl mu/m and longer wavelengths). By combining GaInNAs with GaAs or other wide-gap materials that can be grown on a GaAs substrate, a type-I band lineup is achieved and, thus, very deep quantum wells can be fabricated, especially in the conduction band. Since the electron overflow from the wells to the barrier layers at high temperatures can he suppressed, the novel material of GaInNAs is very attractive to overcome the poor temperature characteristics of conventional long-wavelength laser diodes used for optical fiber communication systems. GaInNAs with excellent crystallinity was grown by gas-source molecular beam epitaxy in which a nitrogen radical was used as the nitrogen source. GaInNAs was applied in both edge-emitting and vertical-cavity surface-emitting lasers (VCSELs) in the long-wavelength range. In edge-emitting laser diodes, operation under room temperature continuous-wave (CW) conditions with record high temperature performance (T/sub 0/=126 K) was achieved. The optical and physical parameters, such as quantum efficiency and gain constant, are also systematically investigated to confirm the applicability of GaInNAs to laser diodes for optical fiber communications. In a VCSEL, successful lasing action was obtained under room-temperature (RT) CW conditions by photopumping with a low threshold pump intensity and a lasing wavelength of 1.22 /spl mu/m.

1.3-μm continuous-wave lasing operation in GaInNAs quantum-well lasers

A 1.3-/spl mu/m continuous wave lasing operation is demonstrated, for the first time, in a GaInNAs quantum-well laser at room temperature. This lasing performance is achieved by increasing the nitrogen content (up to 1%) in GaInNAs quantum layer. It is thus confirmed that this type of laser is suitable for use as a light source for optical fiber communications.

GaInNAs-GaAs long-wavelength vertical-cavity surface-emitting laser diodes

Vertical-cavity surface-emitting laser diodes with GaInNAs-GaAs quantum-well (QW) active layers are demonstrated for the first time. GaInNAs permits the realization of a long-wavelength vertical-cavity laser grown directly on a GaAs substrate. Room-temperature (RT) pulsed operation is achieved, with an active wavelength near 1.18 /spl mu/m, threshold current density of 3.1 kA/cm/sup 2/, slope efficiency of /spl sim/0.04 W/A, and output power above 5 mW for 45-/spl mu/m-diameter devices. Laser oscillation is observed for temperatures at high as 95/spl deg/C.

Extremely large N content (up to 10%) in GaNAs grown by gas-source molecular beam epitaxy

Abstract GaNAs GaP strained single quantum wells are fabricated on GaP wafers by gas-source molecular beam epitaxy in which a nitrogen radical is used as the nitrogen source. The structure and luminescence properties of the quantum wells are investigated by transmission electron microscopy and photoluminescence measurements. The N content in the GaNAs quantum wells was estimated to be about 10%, which is about one order of magnitude larger than previously reported and more than sufficient for fabricating laser diodes on a Si wafer.

Mechanism analysis of improved GaInNAs optical properties through thermal annealing

We investigated the mechanisms of improved GaInNAs optical properties by thermal annealing. The absorption spectra measured for the bulk layer indicated that the large shift in the PL wavelength was probably caused by a bandgap shift in the GaInNAs itself. The cathodeluminescence measurements revealed that the enhancement of the PL intensity was generated by uniform emission from the entire region; in comparison, nonuniform dot-like regions exist in an as-grown GaInNAs layer. These analyses, which is peculiar to this type of material system, should be helpful for further improving the crystal quality, thus helping to enable semiconductor lasers with excellent high-temperature performance.

Ordered structure in OMVPE-grown Ga0.5In0.5P

Abstract The ordered structure of Ga and In in GaInP grown on (001) GaAs by organometallic vapor phase epitaxy (OMVPE) is investigated using high-resolution transmission electron microscopy (TEM). Cross-sectional TEM reveals that the main structure consists of ( 1 2 1 2 1 2 ) and ( 1 2 1 2 1 2 orderings. These orderings are sequences of (111) planes arranged in the order of Ga/P/In/P/ Ga/P/In/P along the [111] and [11 1 ] directions, respectively. The ordered structure may be thermodynamically stable. The OMVPE growth mechanism may partly determine ordering direction in the crystal.

Influence of growth temperature on crystalline structure in Ga0.5In0.5P grown by organometallic vapor phase epitaxy

The relation between growth temperature and ordered structures in Ga0.5In0.5P grown using organometallic vapor phase expitaxy is investigated using transmission electron diffraction, electroreflectance, and Raman scattering measurements. It is found that generation of the ordered structure is not related to the immiscibility of this alloy and that the ordered structures do not simply represent ‘‘sublattice ordering.’’ The anomalous band gap may be a consequence of the variation in the atomic arrangement of neighboring atoms, but not of the long‐range ordered structure itself.

Gas-source MBE of GaInNAs for long-wavelength laser diodes

We have grown GaInNAs using gas source molecular beam epitaxy (GS-MBE) in which a nitrogen radical was used as the nitrogen source. This growth method produces more reactive-N and fewer reactions between the sources. Excellent crystalline quality and luminescence properties of the GaInNAs/GaAs quantum well were confirmed by transmission electron microscopic observation and photoluminescence measurement. We have also succeeded in applying GaInNAs to long-wavelength laser diodes that lased under room temperature continuous wave operation in the 1.3 μm wavelength range suitable for optical fiber communications. Thus, we have experimentally demonstrated that GS-MBE is a suitable method to grow GaInNAs with sufficient quality for device applications.

Effects of rapid thermal annealing on GaInNAs/GaAs multiple quantum wells

Abstract Rapid thermal annealing (RTA) has been performed on GaInNAs/GaAs multiple quantum wells (QW), which were grown by GSMBE using arsine and a RF-plasma nitrogen radical beam source. RTA improves Photoluminescence (PL) intensity. The PL peak also blue-shifts at higher annealing temperatures, most likely due to Ga and In interdiffusion. The optimal annealing temperature is higher for N-containing samples than for N-free GaInAs/GaAs samples. The higher the nitrogen concentration, the larger the shift and proportionally the larger the increase in the PL intensity with RTA, indicating a higher density of non-radiative centers with N incorporation. For the sample consisting of a 2-period Ga 0.7 In 0.3 N 0.02 As 0.98 /GaAs QW and a 2-period Ga 0.7 In 0.3 As/GaAs QW, the room temperature PL intensity of N-containing QW after RTA at 750°C for 10xa0s is comparable to that of N-free QW.

Anomalous temperature dependence of the ordered Ga0.5In0.5P photoluminescence spectrum

The temperature dependence of the photoluminescence spectrum of Ga0.5 In0.5 P/GaAs grown by organometallic vapor phase epitaxy is measured. Samples with a highly long‐range ordered structure show anomalous behavior, where peak energy changes with temperature exhibiting Z‐shape dependence. In the range between 100 and 30 K, peak energy decreases monotonously with decreasing temperature, and below 30 K, begins to increase, splitting into two peaks. The most probable cause of this behavior is crystal defects related to the long‐range ordered structure.