A Study of the Role of Low Energy Ions in Causing Damage to III-V Semiconductors in Practical Ion Etching Systems

[摘要] While dry etching is widely used in the fabrication of advanced III-V semiconductor electronic and optoelectronic devices, the energetic ions employed can inflict damage that impairs the performance of the semiconductor. The avoidance of such material damage is important to ensure the optimum performance of both electronic and optoelectronic devices. The particular aim of the thesis is to study the damage caused by practical etching processes, and so to identify the ion species and mechanisms that cause the damage. The investigation first focused on optical characterisation of the dry etching damage, followed by an effort to integrate it with electrical characterisation. The optical study consisted of photoluminesence (PL) measurements on specially designed quantum well materials. In these material quantum wells of different widths, hence emitting different PL wavelength, have been placed at different depths. Selective etching technique has been applied in order to accumulate damage in the structure without material removal. Thus the measured photoluminescence data, when normalised, provided depth distributions of the damage. An ion implanter is then used to study the effects of different single ion species found in the practical selective etching processes, using the same conditions as in the etching processes. Comparison between the PL results obtained from both etched and ion-implanted samples was made. It has been confirmed that channeling is the main mechanism for the extended depth of the damage in III-V materials studied. Of the ion species studied, molecular ions do not channel, but their fragments may. It is found that Si+ usually deposit on the sample surface. While SiClx etches the semiconductors concerned and causes only low damage, CL+ causes much damage. On the other hand, is CL2+ less damaging. The results therefore point to molecular ions as the desirable species in a low damage process. The experimental results are in excellent agreement with M. Rahman's microscopic theory. The existence of defect diffusion has been confirmed in the presence of strong above-bandgap photon illumination during the etching, but it remains ambiguous in normal etching environments. The investigation moved further to integrating both optical and electrical experiments. Modulation doped quantum well materials have been designed to give PL information and allow measurements of electron transport in the channel. Initial experiments to clarify the interconnection between the optical and electrical damage have been carried out. It was found that electrical quality of the sample deteriorates more significantly than its optical quality. A theoretical explanation of this phenomenon based on trapping of carriers by ion induced trap centres has been presented.

[发布机构] University:University of Glasgow

[关键词] Electrical engineering, Condensed matter physics