Implantation and Dry Etching of Group-III-Nitride Semiconductors

The recent advances in the material quality of the group-III-nitride semiconductors (GaN, A1N, and InN) have led to the demonstration of high-brightness light-emitting diodes, blue laser diodes, and high-frequency transistors, much of which is documented in this issue of MRS Bulletin. While further improvements in the material properties can be expected to enhance device operation, further device advances will also require improved processing technology. In this article, we review developments in two critical processing technologies for photonic and electronic devices: ion implantation and plasma etching. Ion implantation is a technology whereby impurity atoms are introduced into the semiconductor with precise control of concentration and profile. It is widely used in mature semiconductor materials systems such as silicon or gallium arsenide for selective area doping or isolation. Plasma etching is employed to define device features in the semiconductor material with controlled profiles and etch depths. Plasma etching is particularly necessary in the III-nitride materials systems due to the lack of suitable wet-etch chemistries, as will be discussed later.Figure 1 shows a laser-diode structure (after Nakamura) where plasma etching is required to form the laser facets that ideally should be vertical with smooth surfaces. The first III-nitride-based laser diode was fabricated using reactive ion etching (RIE) to form the laser facets but suffered from rough mirror facet surfaces that contributed to scattering loss and a high lasing threshold. This is a prime example of how improved material quality alone will not yield optimum device performance.