Shoji Honda

AlGaInP strained multiple-quantum-well visible laser diodes ( lambda /sub L/<or=630 nm band) with a multiquantum barrier grown on misoriented substrates

Optimization of the misorientation angle of GaAs substrates to prepare multiple quantum wells (MQWS) and multiple quantum barriers (MQBs) with abrupt barrier-well interfaces is reported. The characteristics of AlGaInP strained MQW laser diodes incorporating an MQB grown on misoriented substrates are also investigated, with the aim of developing high-performance 630-nm laser diodes. MQW and MQB with homogeneous periodicity and abrupt barrier-well interfaces were obtained using

AlGaInP visible laser diodes grown on misoriented substrates

AlGaInP laser diodes grown by metal organic chemical vaper deposition (MOCVD) with GaInP active layers have been practically applied in the lasing wavelength range of 667-680nm’) 2 , . However, the lasing wavelength of these devices is not as short as expected from the normal band-gap energy ( 1.92eV) of AlGaInP alloy systems because sublattice ordering is generated during crystal growth4) . In this paper, we report on AlGaInP laser diodes lasing at shorter wavelengths, ir, which the ordering in the active layer was controlled by using n( 1 0 0 ) GaAs substrates with a misorientation towards the ( 0 1 1) direction. Using ( 1 0 0 ) GaAs substrate with a misorientation of 5O off towards the (011) direction, highly reliable laser diodes lasing at 657nm were obtained for the first time without adding A1 to the active layer. Epitaxial growth was carried out by the threestep low pressure MOCVD method. Source materials were AsH3 , PH3 , TMGa, TMA1, and TMIn. The dopant sources were DMZn and SiH, for ptype and ntype layers, respectively. Substrates were n( 100) GaAs with a misorientation towards the ( 0 1 1) direction from 0 to 7O . Figure 1 shows a cross-sectional view of this laser. The stripe width at the bottom of the ridge was 5sm, the p-type cladding layer thickness under the blocking layer was O.Zam, and the active layer thickness was 0.07am. The cavity length was 400am. Figure 2 shows lasing wavelength dependence on the off-angle towards the (011) direction from ( 1 0 0 ) . With an increase in the off-angle, the lasing wavelength became shorter, approaching the band gap energy in GaInP grown by the LPE method” . We believe the shortened lasing wavelngth was achieved by suppressing the formation of the sublattice ordering structure by using the misoriented substrates5) ’ ) . Using (100) GaAs substrate with a misorientation of 7O off towards the (011) direction, device lasing at 655nm was obtained without adding A1 to the active layer. Fig.3 shows the typical I L curve for a laser diode whose wavelength was 657nm. The threshold current was 55mA. and the transverse mode was stable to 10mW. The maximum temperature (Tmax) for CW operation for this device lasing at 657nm was 85C, which was higher than devices lasing at 660nm with an ( Alo . o 5Gao . 9 ) InP active layer grown on a ( 100) substrate. Figure 4 shows the life test results for laser diodes lasing at 657nm under 3mW at 40T. Five devices have been operating without significant degradation for more than 3,000 hours. In summary, transverse-mode stabilized AlGaInP laser diodes were successfully fabricated by a low pressure MOCVD method on n( 100) GaAs substrates with a misorientation towards the ( 0 1 1 ) direction. Using (100) GaAs with a misorientation of 5-7O off towards ( 0 1 1) direction, the lasing wavelength was found to be about 2Onm shorter than those of ( 100) substrates. In the case of the 5O misorientation towards the (01 1) direction, the lasing wavelength was 657nm, the threshold