Origin of void defects in Hg1−xCdxTe grown by molecular beam epitaxy

Void defects were demonstrated to form away from the substrate-epifilm interface during the molecular beam epitaxial growth of mercury cadmium telluride on cadmium zinc telluride substrates. These were smaller in size compared to voids which nucleated at the substrate-epifilm interface, which were also observed. Once nucleated, voids usually replicated all the way to the surface even if the flux ratios were modified to prevent additional nucleation of voids. Occasionally, void defects which close before reaching the top surface without leaving any perturbations on the surface, have also been observed. The voids which form away from the substrate-epi interface, nucleate on defects, frequently hillocks, introduced into the film already grown, leading to formation of defect complexes. These voids can be smaller than 1 µm and appear almost indistinguishable from unaccompanied simple voids. However, these void-hillock complexes displayed a nest of dislocations decorating these defects, which become apparent upon dislocation etching, whereas unaccompanied simple voids did not. The nests could extend as much as 25 µm from the individual void-hillock complex. The density of dislocations within the nest exceeded 5 x 10 6 cm -2 , whereas the dislocation density outside of the nest could decrease to < 2 x 10 5 cm -2 .

Section: Resultssupporting

confidence: 63%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Isolation and control of voids and void-hillocks during molecular beam epitaxial growth of HgCdTe

Chandra¹,

Aqariden²,

Frazier

et al. 2000

“…Large void defects with sizes from several micrometers to tens of micrometers are the most common defect in MBE-grown HgCdTe. They arise as a consequence of Hg-deficient growth conditions, and are called either voids, 1,9,[40][41][42][43][44][45][46][47][48][49][50] crater defects, 6,10,22,23 V-shape 37 The directions of the crosshatched lines as well as the characteristic angles are labeled. The arrows show that the crosshatch lines are sometimes terminated by etch pits, namely dislocations in the crystal.…”

Section: Resultsmentioning

confidence: 99%

Surface Morphology and Defect Formation Mechanisms for HgCdTe (211)B Grown by Molecular Beam Epitaxy

Chang

Becker

Grein

et al. 2008

The surface morphology and crystallinity of HgCdTe films grown by molecular beam epitaxy (MBE) on both CdZnTe and CdTe/Si (211)B substrates were characterized using atomic force microscopy (AFM), as well as scanning (SEM) and transmission (TEM) electron microscopy. Crosshatch patterns and sandybeach-like morphologies were commonly found on MBE (211) HgCdTe epilayers grown on both CdZnTe and CdTe/Si substrates. The patterns were oriented along the 213 Â Ã , 231 Â Ã , and 011 Â Ã directions, which were associated with the intersection between the (211) growth plane and each of the eight equivalent HgCdTe slip planes. This was caused by strain-driven operation of slip in these systems with relative large Schmid factor, and was accompanied by dislocation formation as well as surface strain relief. Surface crater defects were associated with relatively high growth temperature and/or low Hg flux, whereas microtwins were associated with relatively low growth temperature and/or high Hg flux. AFM and electron microscopy were used to reveal the formation mechanisms of these defects. HgCdTe/HgCdTe superlattices with layer composition differences of less than 2% were grown by MBE on CdZnTe substrates in order to clarify the formation mechanisms of void defects. The micrographs directly revealed the spiral nature of growth, hence demonstrating that the formation of void defects could be associated with the Burton, Cabrera, and Frank (BCF) growth mode. Void defects, including microvoids and craters, were caused by screw defect clusters, which could be triggered by Te precipitates, impurities, dust, other contamination or flakes. Needle defects originated from screw defect clusters linearly aligned along the 011 Â Ã directions with opposite Burgers vector directions. They were visible in HgCdTe epilayers grown on interfacial superlattices. Hillocks were generated owing to twin growth of void or needle defects on (111) planes due to low growth temperature and the corresponding insufficient Hg movement on the growth surface. Therefore, in addition to nucleation and growth of HgCdTe in the normal two-dimensional layer growth mode, the BCF growth mode played an important role and should be taken into account during investigation of HgCdTe MBE growth mechanisms.

“…However, MBE growth of HgCdTe is known to be affected by the formation of various macroscopic defects, the most problematic of which are the polycrystalline inclusions commonly referred to as ''voids''. 1,2 Several authors have shown that individual voids in the epitaxial HgCdTe layers can ultimately cause the performance of single pixels and groups of pixels in a focal-plane array (FPA) to be degraded, leading to reduced operability of the array. 3,4 As larger substrates are increasingly utilized to reduce cost by allowing a greater number of FPAs to be fabricated from each wafer, it becomes important to measure and quantify the distribution of defects on each wafer in order to determine its suitability for processing into FPAs before committing to the expense of the fabrication process.…”

Section: Introductionmentioning

confidence: 99%

Full-wafer spatial mapping of macrodefects on HgCdTe epitaxial wafers grown by MBE

Roth

Nosho

Jensen

2006

We have constructed an optical microscopy system to automatically locate, count, and determine the size of polycrystalline ''void'' defects on epitaxial layers of HgCdTe grown on CdZnTe or Si substrates. Void macrodefects are readily imaged because their polycrystalline surface is rough, and consequently they scatter light out of the image under specular reflection imaging conditions. Using a computer-controlled stage to move the wafer, a succession of individual, contiguous bright-field images is recorded over the entire wafer. Each image is analyzed by software to locate and characterize all the lightscattering objects present in the frame. Several different representations of the spatial distribution and size of defects are generated, and these can be presented either as false-color density maps or dot-location maps. In addition, various types of statistics on the defect population and size distributions are also available. These data not only convey overall information on the quality of a given wafer, and as such are quite useful for screening to determine which wafers are suitable for array fabrication, but they also allow inferences to be made concerning the origin or root cause of different classes of defects. Several examples are presented to illustrate the use of full-wafer defect mapping to identify macrodefect problems in HgCdTe growth on CdZnTe that can arise from substrate temperature lateral nonuniformity, nonmatched source flux angular distributions, substrate contamination, and intrinsic substrate imperfections.