Luminescence characteristics of single and multiple aluminum gallium arsenide-gallium arsenide quantum-well heterostructure lasers

Abstract

The luminescence properties of single and multiple A1x Gal-x As-GaAs quantum-well heterostructure lasers grown by meta10rganic chemical vapor deposition (MO-CVD) are shown to differ markedly from those of conventional double heterojunctions because of the two-dimensional nature of the active region. The experimental characteristics of quantum-well recombination radiation are presented and are explained in terms of the properties of quantized carrier motion. Photopumped single quantum-well A1x Gal-x As-GaAs-A1x Gal-x As (x-O. 6, Lz=well width -200 A) heterostructures are shown to operate (77°K) on z confined-particle transitions from the infrared to the red (6885 A, ~A-1300 A, Delta E=hw-E -293 meV). Two fundamental limitations of single quantum-well A1GaAs-GaAs heterostructures are identified. The first is concerned with the highest energy emission obtainable, and is related to the position of the L indirect minima in GaAs. The location of the first indirect conduction band minima (L minima) is determined by a luminescence (emission) technique and is found to be -294 meV above the r band edge at 4.3°K. The second limitation involves the loss of luminescence efficiency as the well thickness Lz approaches the carrier scattering path length lp, where lp -63 A is the electron scattering length with longitudinal optical (LO) phonons. In addition, the band discontinuities between AIGaAs and GaAs are measured by a technique based on the recombination of free electrons in the AIGaAs with bound 'holes in the GaAs well. The carrier collection problem associated with a small single well can be overcome by coupling several thin GaAs quantum layers via thin A1GaAs barriers so as to form a composite active region considerably larger than the scattering length t. These multiple-well structures operate as p lasers continuously at room temperature (CW 3000 K) at energies as high as 145 meV above the GaAs r band edge (hw-Eg -0-145 meV). In addition, data showing CW 3000 K laser operation at photoexcitation threshold levels 2 2 (900W/cm2 , Jth ~375A/cm2 ) comparable to better LPE double heterojunctions and much lower than all previous single or multiple quantum-well heterostructures are presented. The origin of quantum-well recombination radiation below the lowest allowed confined-particle transition is discussed and is identified as phonon-assisted recombination. Phonon-sideband laser data (4.3-3000 K) are presented showing emission at 36, 72, and 108 meV (integer multiples of E-36 meV) below the lowest confined-particle transition. Phonon involvement is also shown to occur throughout the entire direct-gap range of these quantum-well heterostructures. In addition, data are presented indicating that the electron-phonon interaction is enhanced as the number of coupled quantum wells in the active region is increased. A qualitative analysis and discussion of the observed electron-phonon interaction is presented. The origin of this interaction is related to the two-dimensional nature of these structures, and the analysis suggests that stimulated phonon emission is possible in the quantum-well heterostructures of this work.