The formation of twins in 〈111〉 HgCdTe grown by travelling heater method and their effect on device quality

Abstract

Hg 1− x Cd x Te crystals with x∼0.2 were grown by the traveling heater method (THM) in either the [111]A or the 1185 [ 1 1 1 ]B directions using oriented CdTe seeds. Lamellar and double position twins are sometimes formed during the growth of these crystals. The lamellar twinning occurs during the layer-by-layer mode of growth, and is due to high stresses originating from high thermal gradients. Double-position (DP) twins develop under multinucleated growth. This type of growth occurs towards the end of the growth run due to the concave shape of the growth interface at that stage. In crystals grown in the [111]A direction, the lamellar twins, of orientation [ 5 1 1 ]B, are constantly growing at the expense of the original [111]A oriented grain. Growth in the [ 1 1 1 ]B direction, on the other hand, suppresses the growth of the lamellar twin domain. The annihilation is due to arrays of small size interstitial A δ+ ions. Ingots grown in the [ 1 1 1 ]B direction are almost entirely single crystalline, with a growth axis of the <111> type. Photodiodes and capacitors realized on the (111)A plane are markedly superior to those on the lamellar twin plane, ( 5 1 1 )B. The difference is due to a much higher fixed charge and larger fast surface state density in the case of the ( 5 1 1 )B plane. These effects are explained by the lattice structures in the {111} and {511} planes and their possible influence on surface reactivity.