The Lowest Conduction Band Minima of A²B⁴C‐Type Semiconductors

Abstract

Abstract Studies of the influence of hydrostatic pressure up to 6500 kp/cm 2 on the fundamental absorption edge of eleven A 2 B 4 C ‐type compounds of chalcopyrite structure were carried out at room temperature. The large values of d E g /d P ≈ (7.3 to 10.0) × 10 −6 eV kp −1 cm 2 were obtained for CdGeAs 2 , ZnSnAs 2 , ZnGeAs 2 , CdSnP 2 , CdSiAs 2 , ZnSnP 2 , CdGeP 2 (first group of crystals) and much smaller values ≈(—0.7 to + 1.6) × 10 −6 eV kp −1 cm 2 for ZnSiAs 2 , ZnGeP 2 , ZnSiP 2 , and CdSiP 2 (second group of crystals). The comparison of these pressure coefficients with those of Γ 15 ‐Γ 1 and Γ 15 ‐Γ 1 energy gaps in A 3 B 5 compounds leads to the conclusion that the lowest conduction band minima in the first and second groups of A 2 B 4 C crystals are Γ 1 and Γ 3 (or T 1 + T 2 ), respectively. This conclusion is in a good agreement with the calculated band structure of the investigated compounds and is confirmed by the studies of the slope of the fundamental absorption edge. The absorption edge of the first group of crystals is sharp due to the optical transitions Γ 4 → Γ 1 (derived from Γ 15 → Γ 1 in zincblende) and that of the second group of crystals is smooth and is caused by the transitions Γ 4 → Γ 3 or Γ 4 → Γ 1 + T 2 (both correspond to indirect transitions Γ 15 → X 1 in zincblende).