Tetsuya Takeuchi

Blue vertical-cavity surface-emitting lasers based on second-harmonic generation grown on (311)B and (411)A GaAs substrates

We have studied blue vertical-cavity surface-emitting lasers (VCSELs) based on second-harmonic generation (SHG) grown on (411)A and (311)B GaAs substrates in order to investigate suitable substrate orientations for SHG-VCSELs. The comparison among substrate orientations has been made on three parameters, SHG conversion efficiency, transparency current density and gain coefficient. The transparency current density and the gain coefficient are characterized by edge emitting lasers grown on the above substrates. We also discuss the transparency current density and the gain coefficient for (311)A reported previously by Takahashi et al. [M. Takahashi, M. Hirai, K. Fujita, N. Egami, and K. Iga, J. Appl. Phys. 82, 4551 (1997)]. SHG conversion efficiency is 38 and 30% W for SHG-VCSELs grown on (311)B and (411)A substrates, respectively, which is consistent with theory, assuming identical nonlinear coefficients for the A face and B face. Transparency current density for (311)A, (311)B and (411)A is 80, 105 and 60 ...

Continuous‐wave operation of a blue vertical‐cavity surface‐emitting laser based on second‐harmonic generation

An InGaAs/GaAs vertical‐cavity surface‐emitting laser has been fabricated on a (311)B GaAs substrate. Pulsed lasing operation is obtained at room temperature, and continuous‐wave lasing operation is obtained at less than 270 K. From the device, blue laser emission based on second‐harmonic generation is observed. The wavelength of the blue laser emission is 482 nm. At 135 K, its output power is 1 nW under continuous‐wave operation and more than 10 nW under pulsed operation.

Melt-back etching of GaN

Abstract Melt-back etching of GaN is proposed as a novel etching technique and is found to be prospective. The highest etching rate was 1.2 μm/h at a temperature of 1050°C. The etched surface was as good as the surface of an as-grown GaN crystal when the etching temperature is equal to or lower than 900°C, providing a practical etching rate of 0.1 μm/h.

Growth of InGaAs/GaAs strained quantum wells on GaAs(111)B substrates and continuous wave operation of (111)-oriented InGaAs strained quantum well lasers

Abstract The study on the growth conditions of InGaAs/GaAs strained quantum wells on GaAs(111)B substrates by molecular beam epitaxy is described. The crystal quality is evaluated to investigate its dependence on growth temperature and misorientation angle of the substrate. Growth temperature of 550°C and misorientation angle between 1° and 1.5° was found to give high quality InGaAs/GaAs strained quantum wells. Furthermore we have fabricated InGaAs strained quantum well lasers on GaAs(111)B substrates, resulting in a continuous wave operation at room temperature with a threshold current density of 250 A/cm2.

Fabrication of InGaAs Vertical-Cavity Surface-Emitting Laser by Molecular Beam Epitaxy and Its Room-Temperature Operation on (411)A GaAs Substrates

We investigated the optimum molecular beam epitaxy (MBE) growth conditions for fabrication of a high-reflectivity distributed Bragg reflector (DBR) on (411)A GaAs substrates with extremely flat heterointerfaces. A high-reflectivity DBR mirror consisting of AlAs/GaAs was successfully fabricated under the investigated optimum conditions of growth temperature of 580°C with V/III ( As4/Ga) ratio of ~8. Using this high-reflectivity DBR mirror, we succeeded for the first time in the optically pumped pulse operation of InGaAs vertical-cavity surface-emitting lasers (VCSELs) at room temperature on (411)A GaAs substrates with a threshold excitation power density of 11 MW/cm2.

Growth of vertical cavity surface emitting laser material on (3 1 1)B GaAs by MBE

We report on the growth of VCSEL structures on (3 1 1)B GaAs substrates. For the growth of AlGaAs and AlAs, the best morphology and material quality were obtained for growth temperatures > 650°C. Surface morphology and mirror reflectivity degraded significantly at low growth temperatures ( < 600°C). From low-temperature photoluminescence (LTPL), we found a forbidden temperature range for the growth of InGaAs quantum well-active regions on (3 1 1)B substrates between 540 and 560°C. Active region growth temperatures in this range showed low intensity, broad LTPL, and poor laser characteristics. Cross-section TEM measurements show poor homogeneity for material grown in this temperature range. At higher temperatures (580°C), In desorption is greatly increased, so < 520°C was selected as the optimal growth temperature. Even with a non-optimized structure, the first reported VCSELs on (3 1 1)B were fabricated with a pulsed J th = 9 kA/cm 2 at - 40°C and 28 kA/cm 2 at room temperature. At - 40°C, 10 nW of SHG blue light at 485 nm was detected under pulsed conditions, and 2 nW was detected under CW conditions and was visible to the naked eye. By improving the structure we obtained CW lasing at room temperature with 300 A/cm 2 as a broad area laser and 1.4 kA/cm 2 as a VCSEL. A maximum power of 0.55 nW at 490 nm was detected CW at room temperature.

Fabrication of InGaAs vertical-cavity surface-emitting lasers by molecular beam epitaxy on (4 1 1)A GaAs substrates and its room-temperature operation

We investigated the optimum growth conditions for fabrication of a high-reflective distributed Bragg reflector (DBR) with extremely flat heterointerfaces on (41 1)A GaAs substrates by molecular beam epitaxy (MBE). A high-reflective DBR consisting of AlAs/GaAs was successfully fabricated under the investigated optimum conditions of 580°C with V/III (As 4 /Ga) ratio of ∼ 8. Using this high-reflective DBR, we succeeded for the first time in the optically pumped pulse operation of InGaAs vertical-cavity surface-emitting lasers (VCSELs) at room temperature on (4 1 1)A GaAs substrates with improved threshold characteristics compared to conventional (1 0 0) GaAs substrates.

Formation and characterization of porous SiC by anodic oxidation using potassium persulfate solution

The formation process of porous SiC by anodic oxidation was investigated, aiming at the generation of pure white light with a high color rendering index (CRI) and high luminous efficiency. The efficiency of white light emission from porous SiC and its wavelength are strongly dependent on the porous structure such as the average pore size and porosity. In this study, we examined the structure and optical properties of porous SiC by adding potassium persulfate (K2S2O8) as an oxidant in HF solution to control the porosity of porous SiC formed by anodic oxidation. By increasing the amount of the oxidant, we enhanced the integrated light emission intensity of porous SiC to 81 times that of bulk SiC. Through the study of porous SiC we demonstrated that the peak wavelength of the porous SiC could be controlled from 370 to 500 nm. Porous SiC created by anodic oxidation was thus proven to have great potential for realizing high-CRI white light generation using LEDs.

Improved crystalline quality of nonpolar a-plane GaN grown on r-plane patterned sapphire substrate (Conference Presentation)

Nonpolar a-plane GaN (a-GaN) grown on r-plane sapphire substrate is one of the promising materials for eliminating an internal field in III-nitride devices. Thus, a high performance light-emitting diode can be expected by using a high crystalline quality a-GaN. In our study, we realized a high crystalline quality a-GaN by using both patterned sapphire substrate (PSS) and sputtered AlN buffer layer (sp-AlN).nThe PSS had conical patterns with a diameter of 900 nm and a height of 600 nm. The patterns placed with triangular arrangement and an interval of 1000 nm. The 30-nm-thick sp-AlN was deposited on the PSS at 300 oC. Approximately 3.5-um-thick a-GaN was grown by using metal-organic vapor phase epitaxy with optimized growth conditions. The crystalline qualities of the a-GaN were evaluated by X-ray rocking curves full width at half maximum (XRC-FWHM) for both on- and off-axis planes. Moreover, the growth behavior of a-GaN on PSS was characterized by in-situ reflectance and scanning electron microscope.nFor the on-axis GaN (11-20) plane, the XRC-FWHM in the c-axis direction of the a-GaN was 462 arcsec, whereas it was 647 arcsec in the m-axis direction. For the off-axis GaN (10-12) plane, the XRC-FWHM was 990 arcsec. These XRC-FWHMs were significantly decreased compared with that of a-GaN grown on nitridated r-plane flat sapphire. It was suggested the density of defects in a-GaN were decreased by both PSS and sp-AlN. To clarify how to defects in a-GaN decrease by using the PSS and sp-AlN the transmission electron microscope observation was performed.