Masaru Kuramoto

Room-Temperature Continuous-Wave Operation of InGaN Multi-Quantum-Well Laser Diodes Grown on an n-GaN Substrate with a Backside n-Contact

Continuous-wave operation at room-temperature has been demonstrated for InGaN multi-quantum-well (MQW) laser diodes (LDs) grown on low-dislocation-density n-GaN substrates with a backside n-contact. The current, current density and voltage at the lasing threshold were 144 mA, 10.9 kA/cm2 and 10.5 V, respectively, for a 3 µm wide ridge-geometry diode with high-reflection dielectric coated mirrors. Single-transverse-mode emission was observed in the far-field pattern of the LDs and the beam full width at half power in the parallel and perpendicular directions was 6° and 25°, respectively.

Novel Ridge-Type InGaN Multiple-Quantum-Well Laser Diodes Fabricated by Selective Area Re-Growth on n-GaN Substrates

A novel ridge structure fabricated by selective-area epitaxial re-growth is proposed for InGaN multiple-quantum-well (MQW) laser diodes (LDs). This technique is capable of precisely controlling the active ridge width and height, thus enabling stable single tran sverse-mode operation. Together with a backside n-contact on a low-dislocation-density GaN substrate, this structure provides high productivity and performance for GaN-based blue-violet LDs. A stable fundamental transverse mode up to 40 mW was demonstrated for the certain range of ridge dimensions. The minimum aspect ratio of the far-field patterns (FFPs) was about 2.1 in the fabricated ridge-type InGaN MQW LDs.

MBE growth of ZnCdSe and MgZnCdSe alloys on InP substrates with a GaInAs buffer-layer

Abstract Molecular beam epitaxy growth of ZnCdSe and MgZnCdSe systems on (001) InP substrates were investigated. These films were grown on a lattice-matched GaInAs buffer-layer which was ex-situ grown on (001) InP by metalorganic vapor phase epitaxy. During the thermal cleaning process prior to II–VI film growth, group-V molecular beams were not used. By introducing this buffer-layer and lowering the initial growth temperature, the surface morphology of ZnCdSe films changed from rough to specular and the full width at half maximum (FWHM) of the double-crystal (004) X-ray rocking curves of the films decreased from more than 400 arcseconds to 60 arcseconds. The ZnCdSe film showed a very sharp excitonic emission in the 5 K photoluminescence spectra with a FWHM as narrow as 5.5 meV. No emission through deep levels was observed. High-quality MgZnCdSe films were also obtained using a GaInAs buffer-layer.

An alloy semiconductor system with a tailorable band-tail and its application to high-performance laser operation: II. Experimental study on InGaN MQW laser for optimization of differential gain characteristics tuned by In compositional fluctuation

Differential gain and carrier lifetime have been deduced experimentally for InGaN MQWs having different magnitudes of In compositional fluctuation and defect density in the active layer. It has been found that the compositional fluctuation and differential gain show a strong correlation in full accordance with the theoretical model for a band-tail modified by In compositional fluctuation as described in the companion paper (part I). Several laser characteristics, threshold current density, differential gain and response time, were found to be affected by the compositional fluctuation and defect density. The optimization of these growth parameters for producing high-performance blue-violet InGaN MQW LDs is also discussed.

An alloy semiconductor system with a tailorable band-tail and its application to high-performance laser operation : I. A band-states model for an alloy-fluctuated InGaN-material system designed for quantum well laser operation

This paper presents a model for a new class of semiconductor-alloy systems for which the band-tail degree can be tailored. The general model is based on experimentally derived data for the InGaN-alloy system. The temperature dependence of the photoluminescence decay time for an InGaN QW structure is fully analysed, verifying the validity of the model in terms of a band-edge state modified by In compositional variation. We found that the band-edge fluctuation can be grown-in between 3 and 170 meV with a single well defined quasi-Fermi level. This model is then used to predict the laser performance for an alloy-fluctuated materials system. We found that the differential gain and the critical carrier density of the inversion distribution are strongly correlated with the fluctuation but in opposite ways. The utilization of alloy fluctuation is very beneficial for a specific laser operation condition if there is sufficient fluctuation optimization. The experimental verification of the model with regards to the laser operation is described in the companion paper (part II).

Continuous-Wave Operation of InGaN Multi-Quantum-Well Laser Diodes Grown on an n-GaN Substrate with a Backside n-Contact

The continuous-wave operation at room temperature has been demonstrated for InGaN multi-quantum-well (MQW) laser diodes (LDs) grown on facet-initiated epitaxial lateral overgrowth (FIELO) GaN substrates with a backside n-contact. The threshold current was 36 mA, the current density was 5.4 kA/cm2, and the voltage was 7.5 V at the lasing threshold of a 2 μm wide ridge-geometry diode with high-reflection dielectric-coated mirrors. The CW LDs successfully operated up to 80 °C. The optical characteristics for LD structure has been studied and superiority of QW on FIELO GaN over sapphire was demonstrated.

Alloy Semiconductor System with Tailorable Band-Tail: A Band-State Model and Its Verification Using Laser Characteristics of InGaN Material System.

In this paper, we present a model for a new class of semiconductor alloy systems that have a tailorable band-tail. The model is constructed from experimentally derived data on the InGaN alloy system and is extended to a general form. The experiment shows that the possible band-edge fluctuation can be grown-in at least between 3 to 170 meV with a single well-defined quasi-Fermi level. For different degrees of compositional fluctuation grown in the InGaN-quantum-well active layers in laser diodes, the differential gain and compositional fluctuation show a strong correlation in full accordance with the theoretical model proposed here for a band-tail modified by In compositional fluctuation. Possible parameters, including differential gain, are discussed for optimization of laser performance.

Novel RiS-type InGaN MQW laser diodes on FIELO GaN substrates

A novel ridge structure fabricated by selective-area epitaxial growth is proposed for InGaN MQW laser diodes (LDS). This technique is capable of precisely controlling the active ridge width and height, thus enabling stable single transverse-mode operation. Together with a backside n-contact on a low-dislocation-density GaN substrate, this structure provides high productivity and performance for GaN-based blue-violet LDs. The LDs fabricated by this technique have achieved continuous-wave operation at more than 30 mW up to a temperature of 90 degrees C, with a characteristic temperature T0 of 105 K from 20 to 90 degrees C. The laser design and characteristics are discussed in detail.

A Band-Tail Model for InGaN Alloy System and Design for Quantum Well Laser Operation

We have constructed a new theoretical model of compositional fluctuation in InGaN quantum wells (QWs) to investigate the effects of the fluctuation on emission properties and laser performance. The temperature dependence of the photoluminescence decay time for InGaN-QW structures is fully analysed by the model in terms of a band-edge state modified by the compositional variation. This model is then used to predict performance for InGaN-QW lasers. We found that the differential gain and the critical carrier density of the inversion distribution are strongly correlated with the fluctuation but in opposite ways and that the utilisation of the fluctuation is beneficial for a specific laser operation condition. Furthermore, laser diodes with different degrees of fluctuation in the active layers have been fabricated and the predicted dependence of differential gain on the fluctuation has been verified experimentally.