Yutaka Nagai

High-power operation of broad-area laser diodes with GaAs and AlGaAs single quantum wells for Nd:YAG laser pumping

The dependencies of the main lasing characteristics on the facet reflectivity for GaAs and AlGaAs single-quantum-well (SQW) separate-confinement heterostructure (SCH) broad-area laser diodes (LDs) are analyzed. Conditions for the facet reflectivity to achieve optimum values are identified. Under these conditions, the authors obtained respective maximum output powers of 2.9 and 2.6 W for GaAs-SQW and AlGaAs-SQW single-stripe LDs for 150 mu m stripe width, lasing at about 808 nm under a continuous-wave (CW) condition. These LDs were stably operated for over 2000 h under the condition of 1 W constant output power with automatic power control circuits at 45 degrees C in CW operation. >

0.78- and 0.98-/spl mu/m ridge-waveguide lasers buried with AlGaAs confinement layer selectively grown by chloride-assisted MOCVD

The 0.78- and 0.98-/spl mu/m buried-ridge AlGaAs laser diodes (LDs) with a high Al-content AlGaAs confinement layer selectively grown by using a Cl-assisted MOCVD are demonstrated. By employing the AlGaAs confinement layer, the threshold current and the slope efficiency of the 0.78-/spl mu/m LD are improved by /spl sim/40%, compared to those of the conventional loss-guided LD with the GaAs confinement layer. In addition, the stable fundamental mode up to 150 mW and the small astigmatic distance less than 1 /spl mu/m are obtained. The 0.78-/spl mu/m LD also shows the excellent high-power and high-temperature characteristic such as 100 mW CW operation at 100/spl deg/C and the reliable 2,000-hour operation under the condition of 60/spl deg/C and 55 mW. In the 0.98-/spl mu/m LD, the narrow beam with the low aspect ratio of 1.86 and the stable fundamental transverse mode over 200 mW are exhibited. As a result, the 0.98-/spl mu/m LD realizes the high fiber-coupled-power of 148 mW. Moreover, the high-power and high-temperature operation of 150 mW at 90/spl deg/C is obtained. In the preliminary aging test, the LDs have been stably operating for over 900 hours under the condition of 50/spl deg/C and 100 mW. >

Characteristics of laser diodes with a partially intermixed GaAs-AlGaAs quantum well

Laser diodes (LDs) with a partially intermixed quantum-well (QW) active layer are fabricated by Zn out-diffusion from a p-cladding layer to the QW region. The dependencies of the degree of intermixing, measured by the photoluminescence (PL) shift, on Zn concentration of the p-cladding layer (P/sub clad/) and the Al content of the guiding layer (X/sub g/) in a separate-confinement-heterostructure (SCH) are investigated. P/sub clad/ changes in the range from 1/spl times/10 /sup 18/ cm/sup -3/ to 4/spl times/10/sup 18/ cm/sup -3/ and X/sub g/ changes in the range from 0.21-0.37. When P/sub clad/ is 2/spl times/10/sup 18/ cm/sup -3/ and X/sub g/ is 0.37, large bandgap energy shift of 96.1 meV is observed. The lasing wavelengths of the LDs, with the partially intermixed QW, are blue-shifted linearly with increasing P/sub clad/ and X/sub g/. For the bandgap energy shift of 66.8 meV by PL, the threshold current density is increased by 33% from that of the nonintermixed LD. Reliability of LDs with the partially intermixed QW is investigated for the first time. In spite of a large degree of intermixing the reliability of the LD with the partially intermixed QW of 66.8 meV energy shift by PL is the same as the nonintermixed one, which is confirmed by the aging test of 2500 hours at 45/spl deg/C with the output power of 1 W under CW operation. >

Achieving broad-area laser diodes with high output power and single-lobed far-field patterns in the lateral direction by loading a modal reflector

A modal reflector, which consists of a high-reflectivity region surrounded by low-reflectivity regions, is added to the front facet of two types of broad-area laser diodes (LDs) to control the lateral modes. One type of LD is the self-aligned laser with a bent active layer (SBA LD) that has a real index-guiding mechanism. The other is a planar-stripe LD that consists of a Zn-diffused region to confine the current flow and has a gain-guiding mechanism. For the SBA LDs with a modal reflector, stable single-lobed far-field patterns (FFPs) are obtained at up to 0.3 and 0.4 W output powers in continuous wave (CW) operation and pulsed operation, respectively. In addition, for planar-stripe LDs with a modal reflector, stable single-lobed FFPs are obtained at up to 0.4 W in CW operation. The lateral modes inside the cavity are analyzed by utilizing a slit model and FFPs are calculated. Good agreement is found between experimental and calculated FFPs for a large Fresnel number. >

Large-area wafer processing for 0.78-/spl mu/m AlGaAs laser diodes

Large-area wafer processing for buried-ridge loss-guided inner-stripe AlGaAs laser diodes (LDs) has been developed for the first time. High uniformity of ridge waveguides on a 3-in wafer is realized by introducing selective wet etching. The standard deviations of the ridge width and the remaining p-cladding layer thickness on either side of the ridge, which have a great influence on the device characteristics, are 0.07 /spl mu/m and 0.01 /spl mu/m, respectively. As a result, good uniformity of laser characteristics has been obtained, for example, the distribution of full width at half maximum angles of far-field pattern in the direction parallel to the junction plane (/spl theta//sub ///) is only 0.22/spl deg/ (1/spl sigma/) for 1000 chips across a 3-in wafer.<<ETX>>

Uniform and high-power characteristics of AlGaInP visible laser diodes and their four-element arrays fabricated on a three-inch /spl phi/ wafer

The versatile potential of a three-inch diameter wafer processing technology has been successfully demonstrated by the realization of a large number of 680 mn high-power laser diodes (LDs) and their individually addressable four-element arrays on a single wafer at one time. The excellent uniformities of the laser characteristics, such as threshold current, operating current, beam divergences and lasing wavelength have been obtained. The LDs have been operating stably for over 2500 hours under the condition of 60/spl deg/C and 30 mW. In the four-element LD arrays with a junction-up configuration, the linear power-current (P-I) characteristics have been obtained up to 50 mW, even at 50/spl deg/C for each element. Moreover, the thermal crosstalk, defined as the output decrease rate caused by the temperature rise due to neighboring elements operation of 2.9-11.1%, has been realized in the high-power simultaneous operation. >

High-power operation of AlGaAs SQW-SCH broad-area laser diodes for Nd:YAG solid-state laser pumping

AlGaAs single-quantum-well separate-confinement-heterostructure (SQW-SCH) single-stripe broad-area laser diodes (LDs) for Nd:YAG solid-state laser pumping were developed. The high-power operation of the SQW-SCH LD was demonstrated. The maximum output power under continuous wave operation at room temperature was 2.6 W in the range of the Nd:YAG absorption band. Stable operation was also confirmed for over 500 h under the condition of 25 degrees C at 1 W under continuous-wave operation.<<ETX>>

Highly reliable 685-nm 50-mW visible lasers with Zn-diffused windows

High-power, highly reliable 685 nm Zn-diffused type window structure laser diodes (LDs) are developed using 3-inch (phi) wafers. The lasers have exhibited over 7000 hours operation under the condition of 60 degrees Celsius, 50 mW. In addition, over 4000 hours operation under the condition of 60 degrees Celsius, 60 mW is also achieved. These LDs are fabricated by well controlled 3-inch full wafer processing. The window regions near both facets consist of the disordered GaInP wells formed by an open-tube solid-phase Zn-diffusion technique. It is confirmed that highly uniform characteristics are achieved over the 3-inch wafer. Moreover, low astigmatic distances of less than 3 micrometer m are obtained in the range of 3 - 50 mW in spite of the window structure.

Fabrication of broad-area laser diodes on a three-inch wafer by a solid-phase diffusion method

We have developed extremely uniform Zn diffusion on a three-inch GaAs-AlGaAs QW laser wafer by an open tube solid-phase diffusion technique and have applied it to fabrication of broad-area laser diodes (LDs) for the first time using 3-inch full-wafer processing. Excellent uniformity of device characteristics have been obtained on a 3-inch wafer; threshold current distribution along the radial direction of a wafer is 356.2/spl plusmn/8.3 mA (1/spl sigma/), emission wavelength is 879.7/spl plusmn/0.6 nm (1/spl sigma/). Such high uniformity is caused by not only uniform Zn diffusion but also uniform epitaxial layer thickness over a three-inch wafer.<<ETX>>

0.78-0.98 /spl mu/m ridge-waveguide-lasers buried with AlGaAs confinement layer selectively grown by chloride-assisted MOCVD

Ridge-waveguide laser diodes (LDs) buried with an Al/sub 0.7/Ga/sub 0.3/As confinement layer selectively grown by using the Cl-assisted MOCVD have realized, for the first time, reduction of the operating current, stabilization of the lateral mode and the high reliability in the high-power operation.