THE FORMATION OF TWINS IN (111) HGCDTE GROWN BY TRAVELING HEATER METHOD AND THEIR EFFECT ON DEVICE-QUALITY

Hg1-xCdxTe crystals with x approximately 0.2 were grown by the traveli ng heater method (THM) in either the [111]A or the [111BAR]B direction s using oriented CdTe seeds. Lamellar and double position twins are so metimes formed during the growth of these crystals. The lamellar twinn ing occurs during the layer-by-layer mode of growth, and is due to hig h stresses originating from high thermal gradients. Double-position (D P) twins develop under multinucleated growth. This type of growth occu rs towards the end of the growth run due to the concave shape of the g rowth interface at that stage. In crystals grown in the [111]A directi on, the lamellar twins, of orientation [511BAR]B, are constantly growi ng at the expense of the original [111BAR]A oriented grain. Growth in the [111BAR]B direction, on the other hand, suppresses the growth of t he lamellar twin domain. The annihilation is due to arrays of small si ze interstitial A(delta+) ions. Ingots grown in the [111BAR]B directio n are almost entirely single crystalline, with a growth axis of the [1 11] type. Photodiodes and capacitors realized on the (111)A plane are markedly superior to those on the lamellar twin plane, (511BAR)B. The difference is due to a much higher fixed charge and larger fast surfac e state density in the case of the (511BAR)B plane. These effects are explained by the lattice structures in the {111} and {511} planes and their possible influence on surface reactivity.