Basic Research for the Fabrication of Light Emitting Devices Utilizing Quantum Confined Exciton Molecules

本项目的目标是对宽带隙半导体中激子和激子分子的辐射和非辐射复合过程进行基础研究。通过利用时间分辨光致发光(TRPL)光谱详细表征了ZnSe基II-Vl半导体和GaN基III-V半导体的微观结构和宏观光学性质之间的关系，从而促进了这一过程。主要研究成果如下：(1)将光学显微镜与紫外光、皮秒脉冲激光和条纹相机相结合，研制了时空分辨发光仪。利用该系统研究了在解理的ZnSe(110)衬底上生长的自形成的CdSe量子点的发光动力学。在光致发光光谱中观察到波长和寿命都有很大的波动。这可以理解为不同量子点的势垒大小不同，因此反式…(2)用泵浦&探测(P&P)谱方法研究了InGaN多量子阱(MQW)激光基区二极管(LDS)在150fs脉宽下室温下光增益形成的动力学行为。激光二极管由(A)In_&lt；0.1&gt；Ga_&lt；0.9&gt；N-In_&lt；0.02&gt；Ga_&lt；0.98&gt；N多量子阱和(B)In_&lt；0.3&gt；Ga_&lt；0.7&gt；N-In_&lt；0.05&gt；Ga_&lt；0.95&gt；N多量子阱组成，它们的受激发射分别对应于近紫外光(390 Nm)和蓝光(440 Nm)。光学增益是由样品(A)中接近离域的态[最低量子化的多量子阱能级(LQL)]贡献的，而对于样品(B)，它是由相对于LQL的高度局域能级贡献的500 meV。研究发现，在约5ps的时间尺度内，光生载流子迅速(小于1ps)转移到LQL，然后弛豫到局域尾部，从而产生光增益。在较高的光激发下，这种增益谱是饱和的，并且在LQL附近出现了其他带。较少

The objective of this project is to pursue basic research on radiative and nonradiative recombination processes of excitons and exciton molecules in widegap semiconductors. This was facilitated by making detailed characterization on the correlation between microscopic structures and macroscopic optical properties in both ZnSe-based II-Vl semiconductors and GaN-based III-V semiconductors by means of employing time-resolved photoluminescence (TRPL) spectroscopy. The results obtained in the period of 2000 to 2001 can be summarized as follows.(1) Time-space resolved luminescence apparatus was developed by combining optical microscope with ultraviolet optics, pico-second pulsed lasers and streak camera. PL dynamics in self-formed CdSe quantum dots (QDs) grown on cleaved ZnSe (110) substrates was characterized using this system. Large fluctuation of both wavelengths and lifetimes was observed in PL spectra. It can be understood as size of potential confinement differs with QDs, so that trans … More ition energy as well as oscillator strength of excitons is modulated accordingly.(2) Dynamical behavior of optical gain formation has been assessed at room temperature (RT) in the InGaN multi quantum well (MQW) lased Baser diodes (LDs) by employing pump ＆ probe (P&P) spectroscopy under the pulse width of 150 fs. The LDs are composed of (a) In_<0.1>Ga_<0.9>N-In_<0.02>Ga_<0.98>N MQW and (b) In_<0.3>Ga_<0.7>N-In_<0.05>Ga_<0.95>N MQW, whose stimulated emissions correspond to near ultraviolet (390 nm) and blue (440 nm), respectively. The optical gain was contributed from the nearly delocalized states [the lowest-quantized MQW levels (LQL)] in the sample (a), while it was from highly localized levels with respect to LQL by 500 meV for the sample (b). It was found that the photo-generated carriers rapidly (less than 1 ps) transferred to LQL, and then relaxed to the localized tail within the time-scale of about 5 ps, giving rise to the optical gain. Such gain spectra were saturated and other bands appeared in the vicinity of LQL under higher photo-excitation. Less