Analysis of germanium epiready wafers for III–V heteroepitaxy

Abstract

Keywords:Al. Substrates Al. Surface processes A3. Metalorganic vapor-phase epitaxy B2. Semiconducting germanium Frequently, when growing III-V semiconductors on germanium substrates, unexpected differences between nominally identical substrates are encountered. Using atomic force microscopy (AFM), we have analysed a set of germanium substrates sharing the same specifications. The substrates come from the same vendor but different results come about in terms of the morphology of the epilayers produced by the same epitaxial routine (i.e. substrate W\ produced epilayers with good morphology while substrate WX produced epilayers with defects). The morphological analysis has been carried out on (a) epiready substrates; (b) samples after a high-temperature bake at 700 °C; and (c) on the samples after a hydride (PH 3 ) annealing at 640 °C. In the two first stages all substrates (both W\ and WX) show the same good morphology with RMS roughness below 3 A in all cases. It is in the third stage (annealing in PH 3 ) that the morphology degrades and the differences between the samples become apparent. After phosphine exposure at 640 °C, the RMS roughness of both substrates approximately doubles, and their surface appears as full of peaks and valleys on the nanometre scale. Despite the general appearance of the samples being similar, a careful analysis of their surface reveals that the substrates that produce bad morphologies (WX) show higher peaks, and some of their roughness parameters, namely, surface kurtosis and the surface skewness, are considerably degraded.

Optical in situ monitoring of hydrogen desorption from Ge(100) surfaces

“…In the last years, there has been a renewed interest in the characterization of the structural and chemical properties of germanium (100) substrates for applications in microelectronics, 1 nanotechnology, 2 and photovoltaics. [3][4][5][6] A suitable surface preparation (in terms of surface cleanliness, termination, and reconstruction) is crucial for subsequent material and device properties. 7,8 In technologically relevant process ambients, the carrier gas (such as H 2 ) might affect surface reconstruction, 6,9 step formation, 10 and epitaxial growth.…”

XPS as characterization tool for PV: From the substrate to complete III-V multijunction solar cells

“…A good epitaxy starts with a thorough understanding of the substrate surface. The presence of oxides, contaminants or adsorbates can have a key role in the formation of defects during the subsequent lll-V layer growth [2]. Now we present the study carried out on the surface state of commercial epi-ready Ge wafers from two different vendors, namely wafer A and B. Irrespective of the vendor, XPS analysis shows that all the Ge wafers have an oxide layer and reveáis the presence of carbón and, probably chlorine, although the last element seems to appear in a very little quantity.…”

Analysis of the surface state of epi-ready Ge wafers

“…Accordingly, a good epitaxy starts with a thorough understanding of the substrate surface. The presence of oxides, morphological imperfections, contaminants or adsorbates can have a key role in the formation of defects during growth of any layer onto these substrates [2]. Thereby, any characterization technique able to provide insight about the state of the surface prior to epitaxial growth is of utmost interest for the grower, in order to understand and justify the achievement of good (or poor) semiconductor structures and devices.…”