Abstract
The deepness of contactless electroreflectance (CER) probing (d~CER~) is investigated in this work. CER spectra have been measured for various semiconductor structures and compared with photoreflectance (PR) spectra. It has been shown that most of CER signal origins from the sample region which is very close to the sample surface. It has been found that the d~CER~ is much smaller that the penetration depth of the probing beam (d~Ξ»~ βΌ 0.5β1 ΞΌm), d~CER~ ! d~Ξ»~. In addition, for samples containing a sheet of carriers (a two dimensional electron gas at an interface or a deltaβdoped monolayer) the d~CER~ is reduced to the distance from the sample surface to the carrier sheet (e.g. 20 nm). This phenomenon can be called as screening of electromodulation in CER technique. No screening of electromodulation mechanism is observed in PR technique. In addition, the deepness of PR probing (d~PR~) is much bigger than the d~CER~. It means that deeper parts of semiconductor structures (e.g. the buffer layer) can be probed in PR whereas these parts are usually not probed in CER. A different electromodulation mechanism in PR and CER techniques is the origin of various probing deepness for these two techniques. In the case of CER technique, the surface electric field is mainly modulated whereas both surface and interface electric fields can be effectively modulated in the PR technique. In the case of PR technique, the electronβhole pairs can be generated far to the sample surface and hence these carriers can modulate band bending at interfaces which are far to the sample surface, e.g. at the epilayer/buffer interface. (Β© 2007 WILEYβVCH Verlag GmbH & Co. KGaA, Weinheim)