In addition, this damaged layer can be removed by an etchant [39]. We also observe that the coverage of the etched samples decreases upon increasing the RIE durations (from nanopits, nanorods, and finally to nanopyramids), leading to the different roughness values. Optical reflectance has been a sensitive nondestructive Captisol clinical trial method to examine the etched surface morphology. Figure 6 shows the optical reflection spectra with wavelengths from 0.3 to 2 μm for the as-grown and etched samples. The inset in Figure 6 is also a plot

showing the variation of reflectance at 1.55 μm as a function of etching times. The reflectance is found to monotonically decrease with the etching times. The SiGe/Si MQW nanorod sample (i.e., the sample etched for 300 s) show considerably low reflectance over a wide wavelength, only 7.1% and 10.5% at 0.6 and 1.55 μm, respectively. This excellent antireflective characteristic can be buy H 89 attributed to its highly roughened surface. Many techniques including laser- [40] and metal-assisted [41] chemical etching have been reported to fabricate ‘black silicon’ with an ultra-low reflectance. The surface nanoroughening process in

this study could be an alternative approach applied to SiGe-based nanodevices and optoelectronics, Doramapimod ic50 such as metal-oxide-Si tunneling diodes [42], light-emitting diodes [25], and photodetectors operating in the telecommunication range [28]. In addition, the SiGe/Si MQW nanopits and nanorods with well-defined spatial periodicity fabricated in this study would also be potential materials applied to photonic crystals [1] and phototransistors [43]. Figure 6 Optical reflection spectra with wavelengths from 0.3 to 2 μm for the as-grown and etched samples. The spectra were measured at an incident angle of 5°. The inset also shows the variation in reflectance at 1.55 μm as

a function of etching times. Following the slimier fabrication processes, we can also produce the SiGe/Si MQW however nanodots through a resized nanosphere template (Figure 7a). With an appropriate etching time (100 s here), the nanodot arrays consisting of several-period SiGe/Si MQWs can be obtained (Figure 7b). As shown in Figure 7c, although the characteristic PL emission from the MQW nanodot arrays also shows a similar blueshift relative to the as-grown sample, its peak intensity is apparently weaker than that of the as-grown sample possibly due to the severe material loss in the RIE process. We believe that by properly adjusting the process parameters of RIE, the PL characteristics of the MQW nanodots can be improved. Nevertheless, all of these nanofeatures contribute to the potential applications of using NSL combined with RIE to laterally nanopattern SiGe/Si heterostructures. Figure 7 SEM images and PL spectra of the etched MQW samples using a resized nanosphere template. SEM images showing (a) the resized nanospheres with a mean diameter of approximately 480 nm and (b) the resulting SiGe/Si MQW nanodot arrays.