Munehisa Tamura

Low threshold current density operation of GaInAsP-InP laser with multiple reflector microcavities

We propose and demonstrate a new type of semiconductor laser having multiple reflector microcavities for the purpose of low threshold current operation. Very uniform multiple reflector microcavity structure was fabricated by electron beam (EB) lithography and selective wet chemical etching. Due to multiple reflection effect, threshold current density as low as 310 A/cm/sup 2/ (threshold current of 30 mA) was obtained at room temperature with the total cavity length of 64 /spl mu/m and the cavity width of 200 /spl mu/m.<<ETX>>

Surface Damage in GaInAs/GaInAsP/InP Wire Structures Prepared by Substrate-Potential-Controlled Reactive Ion Beam Etching

We investigated photoluminescence intensity dependence on the width of GaInAs/GaInAsP/InP wire structures prepared by substrate-potential-controlled reactive ion beam etching. As a result, the sidewall recombination velocity was estimated to be 2.5 ×103 cm/s under a low excitation power of approximately 1 W/cm2 (Ar+-ion laser, λ=514.5 nm) at 77 K, and was almost the same as that fabricated by wet chemical etching.

Sidewall Recombination Velocity in GaInAsP/InP Quantum-Well Lasers with Wire-like Active Region Fabricated by Wet-Chemical Etching and Organo-Metallic Vapor-Phase-Epitaxial Regrowth

We estimated the nonradiative recombination velocity at the sidewall of GaInAsP/InP quantum-well lasers with narrow wire-like active region, which had been fabricated by wet-chemical etching and two-step organo-metallic vapor-phase-epitaxial (OMVPE) regrowth, from the active region width dependence of spontaneous emission efficiency under current injection. It was shown theoretically that this estimation method of the nonradiative recombination velocity is more accurate than a conventional method using threshold current dependence on the width of an active region, and was confirmed experimentally. The sidewall recombination velocity of 5 stacked multiple-quantum-well and a single-quantum-well structures fabricated by wet-chemical etching and OMVPE regrowth method was estimated to be 1.3 ×103 cm/s and 2.0 ×103 cm/s, respectively, at room temperature, while it was estimated to be very small (less than 10 cm/s) at low temperatures (T = 90 K).

Stripe Direction Dependence of Mesa Angle Formed on (100) InP by Selective Etching using HCl Solution

Stripe direction dependence of mesa angle formed on (100) InP substrate was investigated by selective wet chemical etching using HCl solution with a GaInAs epitaxial mask layer. As a result, it was found that undercut-free etching can be nearly obtained with the stripe formed along the direction whereas large undercut due to anomalous etching occurred along the direction.

Fabrication of GaInAs/GaInAsP/InP multi-quantum-wires and -boxes by substrate-potential-controlled electron cyclotron resonance reactive ion beam etching

GaInAs/GaInAsP multi-quantum-wires and -boxes with the size of 20-30 nm and aspect ratio greater than 6 were fabricated by combining electron beam lithographt and substrate-potential-controlled electron cyclotron resonance (ECR) dry etching. The photoluminescence (PL) at 77K was observed from the buried multi-quantum wires regrown by OMVPE. The PL intensity of the multi-quantum-wire sample, normalized by the space filling factor of the active region, was 66% of that of the multi-quantum-film structure before etching, which confirms the low-damage feature of this fabrication process.

Characterization of Etching Damage in Cl2/H2-Reactive-Ion-Etching of GaInAs/InP Heterostructure.

The etching damage induced by electron-cyclotron-resonance reactive-ion-beam-etching (ECR-RIBE) using pure Cl2 gas and Cl2/H2 mixture gas was characterized by photoluminescence (PL) intensity at 77 K of GaInAs/InP heterostructure. By using a GaInAs/InP multiple layer structure consisting of various thicknesses of GaInAs layers, the PL intensity dependence on the depth from the dry etched surface was obtained and the depth profile was characterized by a Gaussian distribution function with parameters of substrate voltage, mixture ratio of etching gas and substrate temperature. As a result, it was indicated that nonradiative recombination traps induced by ECR-RIBE were reduced to one order of magnitude smaller by adopting a negative bias voltage to the sample, Cl2/H2 mixture gas rather than pure Cl2 gas and a lower substrate temperature.

Photon Recycling Effect in Semiconductor Lasers using Low Dimensional Structures

The photon recycling effect in quantum film, quantum wire, and quantum box has been theoretically investigated using rate equation analysis and the density-matrix method, to obtain further reduction in the threshold current. The threshold reductions due to photon recycling in quantum film, wire, and box, in the case of lattice matched Ga0.47In0.53As/InP, are 40%, 24%, and 0%, respectively, for a fixed cavity loss of lasing mode normalized by the optical confinement factor α L/ξ L=50 cm-1. The estimation also shows that photon recycling is more effective in compressively-strained (CS) Ga0.18In0.82As0.73P0.27/InP quantum structures than in lattice-matched quantum structures. In both cases, the threshold reduction due to photon recycling is larger in the quantum film structure than in quantum wire and box structures, because the deviation between the peaks of the gain and the spontaneous emission spectra is large in the quantum film structure.

Temperature dependences of GaInAsP/InP compressively-strained quantum-wire lasers fabricated by EB lithography and 2-step OMVPE growth

Temperature dependences of 1.5 /spl mu/m wavelength GaInAsP/InP compressively-strained (CS) single-quantum-well lasers with quantum-wire as active region (15-28 nm) were measured and compared with those of quantum-film lasers fabricated on the same wafer. As the result, better lasing properties of the quantum-wire structure lasers over quantum-film lasers were confirmed for the first time at a temperature below 193 K.

Fabrication of InP-based quantum-wires and its application to lasers

Fabrication technologies of GaInAs(P)/InP long-wavelength lasers consisting of quantum-wire active region are investigated. A combination of an electron-beam (EB) lithography, a fine-pattern etching, and succeeding OMVPE regrowth became more or less reliable process, that was confirmed through a low threshold current room-temperature CW operation of strained quasi-quantum-wire lasers. Measurements of photoluminescence (PL) intensity dependence on etched wire width revealed a low-damage property of electron-cyclotron-resonance reactive-ion-beam-etching (ECR-RIBE) with Cl/sub 2/ gas by applying negative acceleration voltage to the sample. An introduction of a surface cleaning process with H/sub 2/ gas just after the Cl/sub 2/ ECR-RIBE was found to be effective for further reduction of damage especially for the wire width from 10 to 40 nm.

Surface damage in GaInAsP/InP wire structures by Cl/sub 2//H/sub 2/-ECR dry etching

We investigated photoluminescence (PL) intensity dependence on the width of GaInAsP/InP wire structures, which were fabricated by an electron cyclotron resonance dry etching (ECR-dry etching) using a mixture of Cl/sub 2//H/sub 2/ (small amount of H/sub 2/ gas is mixed with Cl/sub 2/ gas) as the etching gas. As the result, a reduction of surface damage in GaInAsP/InP wire structures was observed. The S/sup .//spl tau/ product, where S is sidewall recombination velocity and /spl tau/ is the carrier lifetime of the wire structures fabricated using Cl/sub 2//H/sub z/-dry etching and Cl/sub 2/-dry etching were estimated to be 92 nm and 130 nm, respectively, under an excitation power of approximately 100 W/cm/sup 2/ (YAG laser, /spl lambda/=1.06 /spl mu/m) at 296 K.