Zincblende structure compounds

Detailed LEED studies of ZnS (and other zincblende-structure compounds, including ZnTe and CdTe) have established that the (110) surface is reconstructed by movement of the Zn atoms inward (towards the bulk solid) and of the S atoms outward. Displacements of the cation and anion in the uppermost layer by <<0.5 A and in the second layer by 0.1 A compared to the bulk are involved (Duke, 1983). Harrison (1976, 1980) has explained this in terms of an electronic structure model by conversion of half-occupied dangling-bond hybrid orbitals at both Zn and S on the... 

The (110) surface of the zincblende structure compound semiconductors and the ( lOllO) surface of the wurtzite structure compound semiconductors... 

At the same time, calling this a. fit to the bands is very much understating the accomplishment. The set of four parameters in Table 2-1 and the term values in Table 2-2 (all in the Solid State Table) allow calculation of energy bands for any of the homopolar semiconductors or any of the zincblende-structure compounds, as simply for one as for the other, without computers, with consistent accuracy, and without need for a previous accurate calculation for that compound. Only in first-row compounds is there indication of significant uncertainty in the results. Furthermore, as we noted in Table 2-1, the theoretical matrix elements are very nearly equal to the ones obtained by fitting bands thus, if we had plotted bands in Fig. 3-8,a that were based upon purely theoretical parameters, the curves would have been hardly distinguishable. 

Sphalerite (ZincBlende) Structure Compounds (StrukturberichtsymbolB3 Space Group F43m-T )... 

TABLE 1 Lattice parameters of III-N compounds (hexagonal-wurtzite and cubic-zincblende structures). For GaN bulk crystals, the errors indicate variations between various samples, as the measurement accuracy was of about 5 parts per million. For cubic AIN and InN, the given lattice parameters are estimated from bond-lengths of the wurtzite phase. For all epitaxial layers, the given values are relaxed lattice parameters calculated from the measured ones using EQN (1),... 

Fig. 7.5. Calculated (using ab initio pseudopotentials and a Gaussian basis set) equations of state (expressed in terms of total energy versus cell size in atomic volume) for various binary compounds with the P-Sn, rocksalt, and zincblende structures (a) a III-V compound, namely GaAs (b) a prototypical II-Vl compound (c) a prototypical I-VIl compound (after Chelikowsky and Burdett, 1986 reproduced with the publisher s permission).

Structural parameters for atomic adsorption on the (110) and (1010) surfaces of zincblende and wurtzile structure compound semiconductors. The bond length is that of the anion-cation dimer in the first layer. D is the tilt angle in the top layer. The other parameters arc defined by fig. 16. 

Figure 11.26 shows the crystal structures of three ionic compounds CsCl, ZnS, and CaF2. Because Cs is considerably larger than Na, CsCl has the simple cubic lattice. ZnS has the zincblende structure, which is based on the face-centered cubic lattice. If the ions occupy the lattice points, the Zn ions are located one-fourth of the distance along each body diagonal. Other ionic compounds that have the zincblende... 

Silicon carbide (carborundum, SiC) is of especial interest on account of its rich polymorphism, no fewer than six structures being known. As is to be expected, each carbon and silicon atom is tetra-hedrally co-ordinated by four atoms of the other kind, and two of the forms of carborundum have the zincblende and wurtzite structures. The close relationship between these two structures has already been discussed ( 4.13), and is emphasized by the many AX compounds (including ZnS itself) in which both are found. It is illustrated in fig. 8.03, where the cubic zincblende structure has been drawn with one of the cube diagonals vertical and parallel to the principal axis of the wurtzite structure. When viewed in this way it will be seen that both structures can be visualized as formed by the superposition of a series of puckered sheets of atoms, but that in zincblende successive sheets are identical (albeit translated) whereas in wurtzite they differ and are related by a rotation through 180° about the principal axis. In the two structures the sequence of sheets can therefore be symbolized as... 

There is a great number of mostly covalent and tetrahedral binary IV-IV, III-V, II-VI and I-VII semiconductors. Most crystallize in the zincblende structure, but some prefer the wurtzite structure, notably GaN [11,12]. While the bonding in all of these compounds (and their alloys) is mostly covalent, some ionic character is always present because of the difference in electron affinity of the constituent atoms. 

Figure C2.16.3. A plot of the energy gap and lattice constant for the most common III-V compound semiconductors. All the materials shown have cubic (zincblende) structure. Elemental semiconductors. Si and Ge, are included for comparison. The lines connecting binary semiconductors indicate possible ternary compounds with direct gaps. Dashed lines near GaP represent indirect gap regions. The line from InP to a point marked represents the quaternary compound InGaAsP, lattice matched to InP.

Besides group IV, the compounds by the atoms in groups III-V are also semiconductors, such as BN, BP, Bas, AIN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, and InSb. Except for the nitrides, all of these compounds crystallize into the zincblende structure. The nitrides are stable in the wurtzite structure. Meanwhile, the mixrnre crystals made of binary III-V compounds also have semiconducting properties, such as (Ga,Al)As, Ga(As,P),(In,Ga)As, and (In,Ga)(As,P). 

This structure can be obtained from the diamond structure by exchanging two carbon atoms with Zn and S atoms, so that the operation of interchange of two atoms in the primitive unit cell disappears. The zincblende structure is known for different compounds (Agl, AlAs, AlP, AlSb, BAs, BN, BP, BeS, BeSe, BeTe, CdS, CuBr, CuCl, CuF, Cul, GaAs, GaP, GaSb, HgS, HgSe, HgTe, INAs, InP, MnS, MnSe, SiC, ZnSe, ZnTe). For a=5.4093 A the ZnS structure data are the following ... 

With the exception of the Ill-nitrides, the remaining III-V compounds crystallize in the cubic zincblende structure with the lattice constant of undoped GaAs being a = 0.5653 nm at T = 300 K. In this structure each atom is tetragonally coordinated. The [111] direction of the zincblende structure is a polar axis, i.e. this direction and the counter direction are not equivalent. These structures are piezoelectric, resulting in electric fields if the crystal is strained. This is of great importance also for device design of transistors and diodes. 

Isostructural (both compounds have the same structure. For example, both compounds being zincblende structure.)... 

For structures of type D (fiA bridging), three alternatives are possible, all rather rare. Type D1 was first detected in the compound [Co4S2(CO)10].73 More recent examples are [Mo4(NO)4S,3]4 (ll)3 and [Ni9(/i4-S)3(/i3-S)6(PEt3)6]2 (12).74 Type D2 has been found in [SZn4(S2 AsMe2)6]75 and type D3 in [Fe4S(SR)2(CO)12].76 Here the coordination corresponds to that of the zincblende or wurtzite structure. 

The uncertainty concerning the identification of the stabilization mechanism on polar ZnO surfaces is partly due to the lack of atomically resolved STM images. Such images are possible for the nonpolar (1010) and (1120) surfaces [40,41] but have, to our knowledge, not been reported for polar surfaces. The polar cation terminated (111) surface of zincblende compounds typically displays a 2 x 2 reconstruction associated with removal of every fourth surface cation [43,50-52]. This structure is ideally suited to match the charging condition for surface stabilization for this particular surface orientation. The 2x2 reconstruction and the missing surface atoms can directly be observed by STM [52]. In contrast to literature [53], a 2 x 2 reconstruction is also frequently observed in our group for the (0001) surface of wurtzite CdS.4 The reconstruction on the anion terminated (III) surfaces of III—V and II-VI zincblende compounds are considerably more complex. These surfaces... 

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