K. Uomi

GaInNAs: A Novel Material for Long-Wavelength-Range Laser Diodes with Excellent High-Temperature Performance.

We propose a novel material, GaInNAs, that can be formed on GaAs to drastically improve the temperature characteristics (T0) in long-wavelength-range laser diodes. The feasibility of our proposal is demonstrated experimentally.

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.

Gas-source molecular beam epitaxy of GaNxAs1-x using a N radical as the N source

We propose the application of GaNAs as a novel material fabricated on a Si wafer. It is a direct-transition type semiconductor, and can be lattice-matched to Si. Therefore, it is valid for use in the active region of light-emitting devices fabricated on Si. In this letter, GaNAs with a low N content is grown on a GaAs wafer to explore the gas-source molecular beam epitaxy under which a N radical is used as the N source. As a consequence, GaNAs with a N content up to 1.5% is grown, even though the conductance of the N-radical beam cell is fixed at a very low value. The bowing parameter of the bandgap is experimentally evaluated at 18 eV.

InGaAs/InGaAsP MQW electroabsorption modulator integrated with a DFB laser fabricated by band-gap energy control selective area MOCVD

The fabrication and basic characteristics of a InGaAs/InGaAsP multi-quantum-well (MQW) electroabsorption modulator with a novel structure integrated with a distributed-feedback (DFB) laser are presented. A fundamental study was performed on the applicability of the InGaAs/InGaAsP MQW structure to an electroabsorption-type modulator. Efficient attenuation small hole pileup and small chirp characteristics of a discrete modulator based on this MQW structure were demonstrated experimentally. A study of the controllability of in-plane band-gap energy by the use of selective-area metal-organic chemical vapor deposition (MOCVD) was also demonstrated. The modulator was monolithically integrated with a MQW DFB laser of the same material. Using a low-capacitance semi-insulating buried heterostructure, over 14 GHz modulation under high-light-output operations up to +10 dBm was achieved. Modulation at 10 Gb/s with a modulation voltage swing of only 1 V/sub pp/ demonstrates the potential value of this system for 1.55- mu m lightwave communications. >

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.

Modulation-doped multi-quantum well (MD-MQW) lasers. I, Theory

A number of important parameters, such as gain, modulation response and threshold current in modulation-doped multi-quantum-well (MD-MQW) lasers are theoretically investigated. The analytical results indicate that the relaxation oscillation frequency of p-type MD-MQW lasers is enhanced by a factor of 4 compared with DH lasers, and that the linewidth enhancement factor of p-type MD-MQW lasers is reduced to 1/4 that of undoped MQW lasers. The threshold current density of n-type MD-MQW lasers is reduced to 1/2~1/4 that of undoped MQW lasers. The improvements in these properties basically result from the unsatisfied charge neutrality due to the modulation doped effect and from asymmetry in density of states between conduction band and valence bands in III-V materials.

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.

Ultrahigh relaxation oscillation frequency (up to 30 GHz) of highly p‐doped GaAs/GaAlAs multiple quantum well lasers

We have demonstrated a relaxation oscillation frequency (fr) of up to 30 GHz in highly p‐doped (Be=1×1019 cm−3) GaAs/GaAlAs multiple quantum well (MQW) lasers grown by molecular beam epitaxy. This is the highest fr achieved at room temperature for III‐V semiconductor lasers. The high fr is attained by the large differential gain in the p‐doped MQW structure having a low threshold electron density resulted from the excess hole density in addition to the quantum size effect.