梯度掺杂与均匀掺杂GaN光电阴极的对比研究  

Comparison between gradient-doping and uniform-doping GaN photocathodes

作　　者：王晓晖[1] 常本康[1] 钱芸生[1] 高频[1] 张益军[1] 郭向阳[1] 杜晓晴[2] 

机构地区：[1]南京理工大学电子工程与光电技术学院,南京210094 [2]重庆大学光电工程学院,重庆400030

出　　处：《物理学报》2011年第4期715-720,共6页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:60871012;60701013)资助的课题~~

摘　　要：为了提高负电子亲和势(NEA)GaN光电阴极的量子效率,利用金属有机化合物化学气相淀积(MOCVD)外延生长了梯度掺杂反射式GaN光电阴极,其掺杂浓度由体内到表面依次为1×1018cm-3,4×1017cm-3,2×1017cm-3和6×1016cm-3,每个掺杂浓度区域的厚度约为45nm,总的厚度为180nm.在超高真空系统中对梯度掺杂GaN光电阴极进行了激活实验,并与两种厚度为150nm,掺杂浓度分别为1.6×1017cm-3和3×1018cm-3的均匀掺杂反射式GaN光电阴极进行了对比.结果表明:Cs/O激活过程中,梯度掺杂GaN光电阴极光电流的增长速度和最大值都大于均匀掺杂,多信息量测试系统测得梯度掺杂NEAGaN光电阴极的最大量子效率达到了56%左右,比均匀掺杂的高出了近两倍.计算得出梯度掺杂NEAGaN光电阴极在浓度变化区域能带的弯曲量依次为0.024,0.018和0.031eV,能带弯曲所形成的内建电场使其获得了较大的电子漂移扩散长度,并且由于能带总的弯曲量达到了0.073eV,到达表面的光电子具有更高的能量,更容易逸出表面势垒,所以梯度掺杂NEAGaN光电阴极可以获得较高的量子效率.In order to enhance the quantum efficiencies of negative electron affinity（NEA） GaN photocathodes,gradient-doping reflection-mode GaN photocathodes are grown by metal organic chemical vapor deposition（MOCVD） at doping concentrations of 1 × 1018 cm-3,4 × 1017 cm-3,2 × 1017 cm-3 and 6 × 1016 cm-3 from the body to the surface,with the thickness of each doping region being about 45nm and the total thickness of GaN 180 nm.The gradient-doping GaN photocathodes are activated in an ultra-high vacuum system and are compared with two kinds of uniform-doping GaN photocathodes whose thicknesses are both 150 nm and doping concentrations are 1.6 × 1017 cm-3 and 3 × 1018 cm-3 separately.The results show that both the photocurrent growth rate and the maximum photocurrent of the gradient-doping GaN photocathodes are greater than those of the uniform-doping GaN in the Cs /O activation process,and the multi-test system measured maximum quantum efficiency of the gradient-doping NEA GaN photocathode is about 56% which is as high as the double of the uniform-doping.Calculations show that the energy band bendings of the gradient-doping GaN photocathodes are 0.024eV,0.018eV and 0.031eV from the body to the surface,a larger electron drift and diffusion length are gained due to the built-in electric field formed by the energy band bending,because of the 0.073eV total energy band bending the photoelectrons reaching the surface have higher energies and pass through the surface barrier more easily.Therefore the gradient-doping NEA GaN photocathodes have greater quantum efficiencies.

关 键 词：NEAGaN光电阴极 梯度掺杂 量子效率 能带结构 

分 类 号：O462.3[理学—电子物理学]