Study on electrochemical etching of nitride semiconductors

III--氮基，即GaN是已知的化学稳定的。这一结果表明，化学分解过程不能应用于这些半导体。本研究的目标是开发用于III-nitrides作为表面抛光、设备过程中的选择性去除和/或在晶体中的缺陷检测，通过对III-nitrides、特别是GaN的电化学行为的调查。Results obtained are summarized as follows. 1） Electrochemical properties of GaN： Basic electrochemical properties of GaN are similar to those of other semiconductors such as GaAs。由于在电子性能中明显的非均匀性和/或降低密度和/或降低密度，减少，在GaN晶体生长在蓝宝石基底上的纳米管缺陷的存在，对那些样品的电化学数据的复制性非常低。这是对GaN的电化学特性的误解的主要原因，例如作为被动效应.2）GaN的电化学行为和非统一性：通过在电化学行为和电子属性和缺陷之间划分关系，这是有可能评估从电化学数据中获取GaN薄膜的统一性的光电化学行为和非统一性：n型半导体需要额外的孔供应的电化学蚀刻（anodic dissolution）。在氦-Cd激光器（波长325纳米）下的辐射、光电化学蚀刻n型GaN薄膜是在NaOH溶液中制造的。After the etching of current d\~ 1 mA/cm-D1 -2-D1 and etching time of 1 hour， needle-like hillocks with a d\of 10-D110-D1 cm-D1 are formed on the etched surface。从山丘的形状和密度，这是合理的解释，因为像一个针一样的山丘在样本中可能会导致线程的分离。因此，电化学蚀刻成了一种简单而安全的方法，用于破坏III-硝酸盐的检测。

III-nitrides such as GaN are known to be chemically stable. This results in that chemical dissolution processes can not be applied to these semiconductors. The purpose of this study is develop etching technologies for III-nitrides as a surface polishing, selective removal in device process and/or defect detection in the crystals, through the investigation of electrochemical behavior of III-nitrides, especially GaN. Results obtained are summarized as follows.1) Electrochemical properties of GaN: Basic electrochemical properties of GaN are similar to those of other semiconductors such as GaAs. Because of notable non-uniformity in electrical properties and/or defect density and, moreover, presence of nano-pipe defects in GaN crystals grown on sapphire substrates, reproducibility of electrochemical data obtained for those samples are very low. This is a major cause for misunderstandings of electrochemical properties of GaN, such as the passivation effects.2) Electrochemical behavior and non-uniformity of GaN: By clarifying the relationships between electrochemical behavior and electrical properties and presence of defects, it is possible to evaluate the uniformity of GaN films from electrochemical data.3) Photo-electrochemical etching of n-type GaN - Detection of dislocations -: Electrochemical etching (anodic dissolution) of n-type semiconductors needs extra hole supply. Under the He-Cd laser (wavelength 325 nm) irradiation, photo-electrochemical etching of n-type GaN film on sapphire is made in a NaOH solution. After the etching of current density 〜1mA/cmィイD12ィエD1 and etching time of 1 hour, needle-like hillocks with a density of 10ィイD18ィエD1-10ィイD110ィエD1 cmィイD1-2ィエD1 are formed on the etched surface. From the shape and the density of the hillocks, it is reasonable to interpret that such a needle-like hillock is due to a threading dislocation in the samples. Thus, electrochemical etching becomes a simple and safe method for defect detection for III-nitrides.