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Proposal and Estimation of High Polarization and High Quantum Efficiency Semiconductor Photocathode

高偏振高量子效率半导体光电阴极的提议和评估

基本信息

批准号：
06650027
负责人：
HORINAKA Hiromichi
金额：
$ 1.09万
依托单位：
Osaka Prefecture University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

项目摘要

1. GaAs quantum wire structure was proposed as a new photocathode of polarized electron source with high polarization and high quantum efficiency. The anodization was carried out using a (111) oriented p-GaAs substrate (1x10^<18>cm^<-3> : Zn doped) under the conditions of HF concentration of 5-30%, current density of 20-200mA/cm^2 and immersion time of 2-5min. High density and low-size triangle poles (40-90nm in width) were obtained by this simple method when HF concentration was 25%, immersion time 2mins and current density 150mA/cm^2. The shift of the band edge and the splitting of valence band were predicted on the assumption that the quantum wire had the circular cross section.2. The circular polarization of photoluminescence of the p-GaAs quantum wire samples fabricated by anodization method was measured on the excitation of circularly polarized light. Peaks appeared at the higher energy side of the band edge of bulk GaAs in the luminescence polarization spectra. The luminescence polarization exceeded 25% which was the maximum value obtained in bulk GaAs. The luminescence polarization depends on the spin polarization of the conduction band electrons and the splitting of the valence band. These peaks and the enhancement of luminescence polarization were thought to be due to by the band edge shift and the splitting of the valence band.3. The luminescence polarization method using a streak camera is applied to the measurement of the spin relaxation time and the life time of electrons of samples. The temperature dependence of the spin relaxation time of the strained GaAs sample was measured. Electron-hole scattering is thought to be the main mechanism of the spin relaxation of our strained-GaAs photocathode. The spin relaxation time of GaAs quantum wire samples fabricated by the anodization method was measured by using the same method. It was found that the anodized p-GaAs sample had the long spin relaxation time in comparison with original substrate.

1. GaAs量子线结构是一种新型的高极化、高量子效率的极化电子源光电阴极。阳极氧化采用（111）取向的p-GaAs衬底（1 × 10 ~（13）<18>cm ~ 2<-3>：Zn掺杂），HF浓度为5- 30%，电流密度为20- 200 mA/cm ~ 2，浸泡时间为2- 5 min。当HF浓度为25%，浸渍时间为2 min，电流密度为150 mA/cm ^2时，可以得到高密度、小尺寸的三角形电极（宽度为40- 90 nm）。在量子线截面为圆形的假设下，预测了带边的移动和价带的分裂.在圆偏振光激发下，测量了阳极氧化法制备的p-GaAs量子线样品的光致发光圆偏振特性。发光偏振光谱中，GaAs体材料的发光峰出现在带边的高能一侧。发光偏振度超过25%，这是体材料GaAs中获得的最大值。发光极化取决于导带电子的自旋极化和价带的分裂。这些发光峰和发光偏振的增强被认为是由于带边移动和价带的分裂.利用条纹照相机的发光偏振法测量了样品的自旋弛豫时间和电子寿命。测量了应变GaAs样品的自旋弛豫时间随温度的变化关系。电子-空穴散射被认为是应变GaAs光电阴极自旋弛豫的主要机制。用同样的方法测量了阳极氧化法制备的GaAs量子线样品的自旋弛豫时间。结果表明，阳极氧化后的p-GaAs样品具有较长的自旋弛豫时间。