Study on electrochemical etching of nitride semiconductors

III-nitrides such as GaN are known to be be chemically stable. This results in that chemical解决方案不能应用于这些semiconductors. The purpose of this study isdevelop etching technologies for III-nitrides as a surface polishing，selective removal in device process and/or defect detection in the crystalsthrough the investigation of electrochemical behavior of III-nitrides，especially GaN. Results obtained are summarized as follows.1) GaN的Electrochemical性能：基本的GaN electrochemical properties of GaN are similar to those of其他semiconductors such as GaAs.Because of notable non-uniformity in electrical properties and/or defect density and, moreover，nano-pipe defects in GaN crystals grown on sapphire substrates电子数据监测那些样本是非常低的，这是一个主要的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电子性能与电子性能presence of defects，这是可能的，以改进GaN films from electrochemical data.3Photo-electrochemical etching of n-type GaN - Detection of dislocations -Electrochemical etching (anodic dissolution) of n-type semiconductors needs extra hole supply. Underthe He-Cd laser (wavelength 325 nm) irradiation，photo-electrochemical etching of n-type GaN film on sapphire is made in a NaOH solution. After theetching of current density ~ 1ma /cm D12 time of 1 hourneedle-like hillocks with a density of 10 - 18 -10 - 110 - D1- cm - D1-2 - D1 are formed on theetched surface From the shape and the density of the hillocks，这是可能的，因为它包含了这样的需要-like hillock is due to a threading dislocationthe samples. Thus，electrochemical etching becomes a simple and safe method for defect detection for III-nitrides。

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.