Reduction of Dislocation Density by Producing Novel Structures

HgCdTe, because of its narrow band gap and low dark current, is the infrared detector material of choice for several military and commercial applications. CdZnTe is the substrate of choice for HgCdTe as it can be lattice matched, resulting in low-defect-density epitaxy. Being often small and not circular, layers grown on CdZnTe are difficult to process in standard semiconductor equipment. Furthermore, CdZnTe can often be very expensive. Alternate inexpensive large circular substrates, such as silicon or gallium arsenide, are needed to scale HgCdTe detector production. Growth of HgCdTe on these alternate substrates has its own difficulty, namely large lattice mismatch (19% for Si and 14% for GaAs). This large mismatch results in high defect density and reduced detector performance. In this paper we discuss ways to reduce the effects of dislocations by gettering these defects to the edge of a reticulated structure. These reticulated surfaces enable stress-free regions for dislocations to glide to. In this work, a novel structure was developed that allows for etch pit density of less than 4 × 105/cm2 for HgCdTe-on-Si. This is almost two orders of magnitude less than the as-grown etch pit density of 1.1 × 107/cm2. This value of 3.35 × 105/cm2 is below the <1 × 106/cm2 or even the better <5 × 105/cm2 target for this research, making HgCdTe-on- alternate substrate density much more like that of HgCdTe-on-CdZnTe.