Lasing mechanisms in high-quality T-shaped quantum-wire lasers

采用分子束外延技术，通过劈裂边过生长和生长中断退火，制备了20条14 nm × 6 nm的T型量子线激光器结构，每条量子线具有原子级平坦的界面。我们用自行研制的马达扫描系统对这些激光器结构进行了PL扫描测量、与激发功率有关的PL测量、光激发的激光测量、Shaklee方法和Hakki-Paoli方法的增益测量。我们对仅包含一条具有相同横截面尺寸的量子线的单线激光器结构进行了类似的测量。我们还对一个n型调制掺杂的单量子线结构进行了详细的PL扫描测量，通过PL扫描测量，我们能够从具有较大PL宽度或具有局域态的区域中选择PL宽度为1-1.5meV的高质量量子线区域。从PLE测量结果，可靠的分配一维自由激子和连续态的基础上进行了比较，严格的理论计算，包括库仑相互作用。首次测量了连续态的线形。最后，依赖于激发功率的PL测量证实了线中双激子和电子-空穴等离子体的形成。与激光实验数据的比较表明，激光增益的来源不是以前所说的自由激子，而是强库仑关联的电子空穴等离子体。

T-shaped quantum wire laser structures containing 20 wires of 14nmx6nm size each with atomically flat interfaces have been fabricated by cleaved edge overgrowth with growth interrupt annealing in MBE. We studied these laser structures by PL scanning measurements with our home made motor scanning system, excitation power dependent PL measurements, lasing measurements with optical excitations, gain measurements by Shaklee method and Hakki-Paoli method. We made similar measurements for a single wire laser structures containing only one quantum wire with the same cross-sectional size. We also performed detailed PL scanning measurements for an n-type modulation-doped single quantum wire structure with a gate to tune one-dimensional electron gas density like a FET.Thanks to the PL scanning measurements we were able to select high-quality quantum wire regions with PL width of 1-1.5meV from regions with larger PL width or with localized states. From PLE measurement results, reliable assignments to one-dimensional free excitons and continuum states have been done on the basis of comparison with rigorous theoretical calculations including the Coulomb interactions. Line shape of continuum state was measured for the first time.Finally, excitation power dependent PL measurements have demonstrated formation of biexcitons and electron-hole plasmas in the wires. Comparison with the lasing data have shown that the origins of gain in lasing are not free excitons that were claimed before, but are strongly-Coulomb correlated electron-hole plasmas.