极化诱导实现AlGaN薄膜材料中的超高电子浓度(1020cm-3)掺杂

材料的载流子浓度和迁移率是影响器件性能的关键因素, 变温Hall测试结果证明杂质掺杂AlGaN中的载流子浓度和迁移率随温度 降低而减小.然而极化诱导掺杂的载流子浓度和迁移率不受温度变化的影响.以准绝缘 的GaN体材料作为衬底, 在组分分层渐变的AlGaN中实现的极化诱导掺杂浓度 仅仅在10¹⁷ cm^-3数量级甚至更低. 本研究采用载流子浓度为10¹⁶ cm^-3量级的非有意n型掺杂GaN模板为衬底, 用极化诱导掺杂技术在分子束外延生长的AlGaN薄膜材料中实现了高 达10²⁰ cm^-3 量级的超高电子浓度. 准绝缘的体材GaN半导体作衬底时, 只有表面自由电子作为极化掺杂源, 而非有意掺杂的GaN模板衬底除了提供表面自由电子外,还能为极化电场 提供更多的自由电子"源", 从而实现超高载流子浓度的n型掺杂.

Polarization induced ultra-high electron concentration up to 1020 cm-3 in graded AlGaN

Carrier concentration and mobility of materials are key factors affecting device performance. Hall tests at different temperatures demonstrate that the carrier concentration and mobility in impurity-doped AlGaN decrease with temperature decreasing. However, carrier concentration and mobility obtained by polarization-induced doping are independent of temperature. Using quasi-insulating GaN as substrate, the electron concentration obtained in the linearly graded AlGaN film through impurity-doping is only 10^-17 cm^-3 or less. In this study, using unintentional impurity doped (n-type, 10^-16 cm^-3) GaN template, graded AlGaN film is grown by molecular beam epitaxial, in which polarization induced ultra-high electron concentration is up to 10²⁰ cm^-3 in graded AlGaN film without using any dopant. Using quasi-insulating GaN as substrate, only the surface of the free electrons serves as polarization dopant, while unintentionally doped GaN template is used as a substrate, in addition to free electrons on surface/interface, it is also reasonable to surmise more negative charges attracted by polarization electric field to be the source of polarization doping, in the unintentional doped GaN template, thereby achieving an ultra-high carrier concentration via polarization induced n-type doping.