Chemical trends of stability and band alignment of lattice-matched II-VI/III-V semiconductor interfaces

Using the first-principles density functional theory method, we systematically investigate the structural and electronic properties of heterovalent interfaces of the lattice-matched II-VI/III-V semiconductors, i.e., ZnTe/GaSb, ZnSe/GaAs, ZnS/GaP, and ZnO/GaN. We find that, independent of the orientations, the heterovalent superlattices with period $n=6$ are energetically more favorable to form nonpolar interfaces. For the [001] interface, the stable nonpolar interfaces are formed by mixing 50% group-III with 50% group-II atoms or by mixing 50% group-V with 50% group-VI atoms; for the [111] nonpolar interfaces, the mixings are 25% group-III (II) and 75% group-II (III) atoms or 25% group-V (VI) and 75% group-VI (V) atoms. For all the nonpolar interfaces, the [110] interface has the lowest interfacial energy because it has the minimum number of II-V or III-VI “wrong bonds” per unit interfacial area. The interfacial energy increases when the atomic number of the elements decreases, except for the ZnO/GaN system. The band alignments between the II-VI and III-V compounds are drastically different depending on whether they have mixed-cation or mixed-anion interfaces, but the averaged values are nearly independent of the orientations. Similarly, other than ZnO/GaN, the valence-band offsets also increase as the atomic number of the elements decreases. The abnormal trends in interfacial energy and band alignment for ZnO/GaN are primarily attributed to the very short bond lengths in this system. The underlying physics behind these trends are explained.

Figure 1

Schematic plots of (a) [100], (b) [110], and (c) [111] (II-${\mathrm{VI})}_6$/(III-${\mathrm{V})}_6$ superlattices. The right side of the plot shows the lateral atomic arrangements parallel to the interface. $a_1$ and $a_2$ are the basis vectors of the lateral plane. The green, orange, gray, and dark yellow balls indicate the group-III, -V, -II, and -VI atoms, respectively. The color scheme is the same for all figures in the paper.

Figure 2

Interfacial energies ($\mathrm{meV}/{\AA }^2)$ of ZnTe/GaSb (a) [001], (b) [110], and (c) [111] interfaces calculated for all nonequivalent interfacial atomic configurations.

Figure 3

Atomic configurations of (GaSb)/(ZnTe) [001] interfaces corresponding to A, B, C, D, and E points in Fig. 2. Structures A and B are the mixed-cation interfaces, C and D are the mixed-anion interfaces, and E is for a sharp interface.

Figure 4

Corresponding potential distributions of interfacial structures A, B, C, D, and E along growth orientation for the (GaSb)/(ZnTe) [001] $\sqrt{2}\times \sqrt{2}$ superlattices. The red lines indicate the top of the potential along the growth direction of the superlattice and show schematically whether or not there is an electric field through the superlattice. This scheme is the same for Figs. 6 and 8 in this paper.

Figure 5

Total density of states (DOS) of structures A, B, C, D, and E for the (GaSb)/(ZnTe) [001] superlattices. The Fermi level is set to be 0 eV.

Figure 6

Atomic configuration (the upper panel) and potential distribution (the bottom panel) of structure F of the ZnTe/GaSb [110] $1\times 1$ superlattice.

Figure 7

Atomic structures of ZnTe/GaSb [111] $2\times 2$ interfaces corresponding to G, H, I, J, K, L, M, N, and O sites in Fig. 2. Structures G, H, I, and J are the mixed-cation interfaces with different symmetries, and K, L, M, and N are the mixed-anion interfaces with different symmetries. As a comparison, we also list the abrupt interface (structure O).

Figure 8

Potential distributions for the mixed-cation interfaces [i.e., G, H, I, and J in Fig. 2] and mixed-anion interfaces [K, L, M, and N in Fig. 2], respectively, along the [111] direction for the (GaSb)/(ZnTe) [111] $2\times 2$ superlattices. As a comparison, we also show the potential distributions for the pure interface (structure O).

Figure 9

Schematic Coulomb interactions of ZnTe/GaSb [001] superlattice systems in forming (a) polar and (b) nonpolar interfaces.