We report on the OMVPE (organometallic vapor phase epitaxial) growth and characterization of AlGaInN heterostructures and laser diodes, including measurements of electrical properties (Hall), structural characteristics (x-ray diffraction and TEM), and room temperature, pulsed laser operation of a 10- quantum well InGaN/AlGaN heterostructure.
The utilization of visible laser diodes for laser printing is discussed. First, the characteristics of a multiple- element array of single-mode, individually-addressed red (AlGaInP) laser diodes is described. The benefit of shorter- wavelength blue lasers is then evaluated. Finally, towards the realization of a blue laser diode, we describe results for AlGaInN and its heterostructures, which have been grown by OMVPE and characterized, including electrical injection and optical pumping of InGaN/AlGaN heterostructures.
Polarization characteristics of TE/TM cross-polarization semiconductor laser diodes are discussed in this paper. Broad area lasers fabricated from tensile strained In<SUB>0.5+(delta</SUB> )Ga<SUB>0.5-(delta</SUB> )P/(AlGa)<SUB>0.5</SUB>In<SUB>0.5</SUB>P quantum well laser structures oscillate in TE/TM dual polarizations. Polarization dominance changes from TE to TM as the cavity length of the laser is increased from 250 micrometers to 650 micrometers. The polarization-dependent gain property of a tensile-strained quantum well laser is analyzed from a simple theoretical model. In a slightly tensile strain quantum well, where light-hole and heavy-hole ground states are nearly degenerate in the valence band due to the strain and quantization effect, gain is provided for TM and TE modes simultaneously, and the two mode gain curves cross at certain injection level. Polarization switching is made possible by changing the threshold gain of the laser. The threshold gain dependent polarization switching is utilized to fabricate closely spaced independently-addressable dual beam cross polarization lasers. Results on 650 nm broad area dual beam cross polarization laser are presented. For dual polarization infrared lasers, a dual quantum well structure in which gains for TE and TM modes are provided by lattice-matched and tensile-strained quantum wells separately is designed. Eight-hundred-thirty-five nm broad area laser fabricated from a GaAs and GaAs<SUB>0.95</SUB>P<SUB>0.05</SUB> dual quantum well structure oscillating in TE/TM dual polarizations is demonstrated.
The temperature dependence of threshold current and quantum efficiency for Ga<SUB>x</SUB>In<SUB>1- x</SUB>P (x equals 0.4, 0.6; (lambda) equals 680, 633 nm) single 80 angstrom quantum well lasers is analyzed using a model for the electron leakage current. This model fits the experimental data, correctly describing the rapid increase in threshold and drop in quantum eficiency as temperature increases. Also it indicates that the drift component of the electron leakage current is important, because of the poor p-type conductivity in AlGaInP. In addition, a single quantum well Ga<SUB>0.5+(delta</SUB> )In<SUB>0.5-(delta</SUB> )P/(AlGa)<SUB>0.5</SUB>P laser structure is demonstrated, which can provide similar gain in both polarizations. The slightly-tensile- strained quantum well has the light hole ground state, which gives the lowest transparency current for TM-mode gain. However, the TE-mode gain is dominant at high drive currents. The gain-current relationships have been characterized for each polarization, and found to cross at a modal gain value of 25 cm<SUP>-1</SUP>. Lasers whose threshold gain is near this crossover value were found to emit in either one or both polarizations, with a very wide range of polarization assymetry possible. A simple QW gain model can be used to describe this behavior.
The properties and low pressure organometallic vapor phase epitaxy of Ga<SUB>x</SUB>In$1-x)P/(AlGa)<SUB>0.5</SUB>In<SUB>0.5</SUB>P quantum well (QW) laser diode heterostructures with Al<SUB>0.5</SUB>In<SUB>0.5</SUB>P cladding layers, and having wavelength 614 < (lambda) < 754 nm, are described. At longer wavelengths ((lambda) > 660 nm), threshold current densities under 200 A/cm<SUP>2</SUP> and efficiencies greater than 75% result form a biaxially- compressed GaInP QW active region. Although short wavelength laser performance is diminished by the poor electron confinement afforded by AlGaInP heterostructures, good 630 nm band performance is achieved with strained, single QW active regions. The wavelength range may also be expanded into the previously difficult 700-nm band, by including InGaAsP or AlGaAsP QWs.
High power visible semiconductor laser diodes are reported at wavelengths ranging from 620 nm to 690 nm. Broad area laser diodes exhibit peak cw output powers of 3.8 W from a 250 micrometers aperture at 688 nm and > 1 W cw at 636 nm from a 100 micrometers aperture. Monolithic 1 cm arrays with a 24% filling factor provide output powers of 30 W cw at 687 nm. Single mode lasers in the 620 nm wavelength band emit > 50 mW and operate at temperatures up to 80 degree(s)C.
We report recent results in high power visible diode lasers operating in both the 680 nm band and the 630 nm band. Continuous wave (CW) output powers in excess of 1 W from a 100 p.m aperture and 8.5Wfrom a monolithic 8 mm bar have been obtained in the 680 nm band. At 633 nm, 900 mW have been measured from a 100 jim wide aperture and 3 W from a 1 cm bar. We also discuss the temperature and length dependence of the threshold current density and external efficiency.