Photopumping of quantum well heterostructures at high or low Q: phonon-assisted laser operation

Data are presented showing the basic difference in the stimulated emission spectrum of a photopumped Al{sub x}Ga{sub 1-x}As-GaAs or Al{sub y}Ga{sub 1-y}As-GaAs-In{sub x}Ga{sub 1-x} As quantum well heterostructure (QWH) heat sunk in a high-Q versus a low-Q cavity configuration. In the high-Q case a 1-2 {mu}m thick narrow (25-50 {mu}m) cleaved rectangle, with the (100) GaAs substrate removed, is heat sunk compressed in In under a sapphire, giving a high cavity photon lifetime because of metal reflectors folded up along the four samples edges. In the latter case (low Q) the (100) QWH rectangle is clamped under a sapphire into simple contact with Au, leaving the four cleaved (110) sample edges lossy and yielding, compared to carrier thermalization times, a short resonator photon lifetime across the sample. For photopumping (77 K, Ar{sup +} laser, 5145 {angstrom}) of a low-Q QWH sample, only lower energy recombination radiation is observed, including phonon-assisted laser operation (provided that the QWH is designed with good carrier, phonon, and photon confinement and with low alloy composition Al{sub x}Ga{sub 1-x}As thermalization layers generating GaAs, like phonons near the QW). For photopumping of an otherwise similar QWH heat sunk in the high-Q configuration (long photon lifetime across themore » sample), recombination at higher energy can compete with carrier thermalization, and laser operation is observed on the confined-particle transitions, thus making unambiguous the identification of phonon sideband laser operation. Comparison of various QWHs heat sunk in the form of low-Q or high-Q resonators reveals the heterostructure layer configurations appropriate for phonon-assisted laser operation.« less