Nondestructive Characterization of Residual Threading Dislocation Density in HgCdTe Layers Grown on CdZnTe by Liquid-Phase Epitaxy

Abstract

The performance of mercury cadmium telluride (MCT)-based infrared (IR) focal-plane arrays is closely related to the crystalline perfection of the HgCdTe thin film. In this work, Te-rich, (111)B-oriented HgCdTe epilayers grown by liquid-phase epitaxy on CdZnTe substrates have been studied. Surface atomic steps are shown on as-grown MCT materials using atomic force microscopy (AFM) and white-light interferometry (WLI), suggesting step-flow growth. Locally, quasiperfect surface spirals are also evidenced. A demonstration is given that these spirals are related to the emergence of almost pure screw threading dislocations. A nondestructive and quantitative technique to measure the threading dislocation density is proposed. The technique consists of counting the surface spirals on the as-grown MCT surface from images obtained by either AFM or WLI measurements. The benefits and drawbacks of both destructive—chemical etching of HgCdTe dislocations—and nondestructive surface imaging techniques are compared. The nature of defects is also discussed. Finally, state-of-the-art threading dislocation densities in the low 10⁴ cm⁻² range are evidenced by both etch pit density (EPD) and surface imaging measurements.