透射式GaAs光电阴极荧光谱特性研究

Study on Fluorescence of Transparent GaAs Cathode

测量了透射式GaAs光电阴极四层、二层结构组件和三代像增强器光电阴极的荧光谱。激发光的波长分别为514.5 nm和785 nm。测量结果表明,GaAs外延层荧光谱的峰值波长较GaAs衬底荧光峰值波长长。当GaAs阴极四层结构组件变为二层结构组件时,GaAs发射层的荧光谱峰值波长向长波方向移动。将GaAs阴极二层结构组件减薄激活之后,GaAs阴极发射层的荧光谱峰值波长向短波方向移动。三代像增强器GaAs阴极组件在制作过程中荧光谱峰值波长变化的原因主要是GaAs发射层内部晶格存在应变,因此当四层GaAs阴极组件变为二层GaAs阴极组件之后,由于GaAs发射层内部晶格应变状态的变化,致使荧光谱的峰值波长向长波方向移动。当二层GaAs阴极组件经过减薄、热清洗和激活之后,由于GaAs发射层内部应力的释放,应变在一定程度上得到消除,因此GaAs发射层的荧光谱峰值波长又向短波方向移动。通常情况下,GaAs材料的荧光谱是一条高斯型的曲线,但对三代管GaAs阴极组件而言,当GaAs发射层中存在不均匀的晶格应变时,其荧光谱曲线在峰值附近会出现不规则的形状,而当不均匀的晶格应变消除后,荧光谱曲线会恢复到正常的形状。所以GaAs发射层中存在的应变会通过荧光谱反映出来,这样在GaAs光电阴极的制作过程中,除了通过测量积分光荧光来评价GaAs光电阴极的制作过程之外,还可以通过测量GaAs光电阴极荧光谱的峰值波长变化来监控GaAs光电阴极的制作过程。

The fluorescence spectra of transparent GaAs photocathode of four layer, two layer structure assembly and the third generation image intensifier are measured. The wavelengths of the exciting light are respectively 514.5 nm and 785 nm. The measurement results show that the peak wavelength of fluorescence spectrum of the GaAs epitaxial layer is longer than that of GaAs substrate fluorescence. When the cathode of GaAs four-layer structure assembly were made into two-layer structure assembly, peak wavelength of fluorescence of GaAs emission layer shifts toward the long wavelength. After the GaAs cathode of two-layer structure assembly was thinner and activated by Cs-O, the peak wavelength of fluorescence of GaAs cathode emissive layer shifted to short wavelength direction. While the third generation image intensifier GaAs cathode assembly is in the production process, the major cause of its peak wavelength variation of fluorescence spectrum is the internal lattice strain of GaAs emission layer, so when the four layers of the GaAs photocathode was made into two layers, due to changes in GaAs emission layer internal lattice strain state, the peak wavelength of fluorescence spectra is moved to long wavelength direction. After thinning, heat cleaning and activation to the two layers of the GaAs emission layer, due to internal stress release, strain can be eliminated to a certain extent, so the peak wavelength of GaAs fluorescence emission layer is shifted to short wavelength direction. Typically, the fluorescent spectrum of GaAs material is a Gauss curve, but the GaAs cathode assembly of the third generation image intensifier, when in the presence of no uniform lattice strain of GaAs emission layer, the fluorescence spectrum curves in the peak will occur near the irregular shape, and when the lattice strain in homogeneity is eliminated, fluorescence spectral curve will be restored to the normal shape. The strain of the GaAs emissive layer will be reflected by fluorescence spectrum, so in the process of making GaAs photocathode, in addition to measuring the integrated fluorescence of GaAs photocathode, the peak wavelength change of GaAs fluorescent spectrum can also be measured in order to monitor GaAs photocathode process.