Zincblende semiconductors

Zinc antimonide, 3 44, 53—54 Zinc atomizing process, 26 598 Zinc baths, 9 828-829, 830t Zincblende semiconductors, 22 141 band structure of, 22 142-144 transport properties of, 22 148, 149t Zinc borates, 4 282-283 Zinc brass... 

The same analysis that has been made here for the zincblende semiconductors can of course be carried out for the wurtzitc structure. For comparison with experiment, another approach is simpler that is to compare the formulae obtained here with effective cubic elastic constants, which were obtained by Marlin (1972b). These were estimates of what the constants of wurtzitc compounds would... 

An examination of the terms for the g values will show that these simply represent the interference behavior of the electron waves with given wave vectors k interacting with atoms at positions defined by the real-space vectors d and at the origin. The g values include the free-electron-like behavior of Chapter 2. The calculation of the g factors becomes more complex when second-nearest neighbors and beyond are included, but the method is the same. The energy of an electron with wave vector k is the determinant of a matrix representing the energies of all possible orbital pairs. For example, for a zincblende semiconductor with no d-orbitals the LCAO matrix is [c.f Ref 4] ... 

The configurational entropy for a system with clustering described by the qj distribution probabilities above has been estimated for a zincblende semiconductor alloy to be a modified regular solution entropy, [6]... 

There is a great number of mostly covalent and tetraliedral binary IV-IV, III-V, II-VI and I-VII semiconductors. Most crystallize in tire zincblende stmcture, but some prefer tire wairtzite stmcture, notably GaN [H, 12]. Wlrile tire bonding in all of tliese compounds (and tlieir alloys) is mostly covalent, some ionic character is always present because of tire difference in electron affinity of tire constituent atoms. 

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

Table 1. Physical Properties of the Cubic Zincblende Structure III—V and II—VI Semiconductors...

The remark just made suggests that a natural place to begin our discussion of equilibrium equations is with the occupation of different charge states. Let a hydrogen in charge state i(i = +, 0, or - ) have possible minimum-energy positions in each unit cell, of volume O0, of the silicon lattice. (O0 contains two Si atoms, so our equations below will be applicable also to zincblende-type semiconductors.) To account for spin degener-ancies, vibrational excitations, etc., let us define the partition function... 

Detailed analysis of x-ray diffractometry reveals the local structure of semiconductor clusters. Bawendi et al. (21) applied the method to CdSe nanoclusters of 3.5-4.0 nm. They concluded that these clusters have a mixture of crystalline structures intermediate between zincblende and wurtzite, on the basis of detailed simulation studies taking the thermal fluctuation into account. Conventional diffractometry could overlook the coexistence of wurtzite component. 

This article focuses primarily on the properties of the most extensively studied III—V and II—VI compound semiconductors and is presented in five sections (/) a brief summary of the physical (mechanical and electrical) properties of the zincblende cubic semiconductors (2) a description of the metal organic chemical vapor deposition (MOCVD) process. MOCVD is the preferred technology for the commercial growth of most heteroepitaxial semiconductor material (J) the physics and (4) applications of electronic and photonic devices and (3) the fabrication process technology in use to create both electronic and photonic devices and circuits. 

By the use of mainly LEED and lately ion scattering techniques the location of many atomic adsorbates, their bond distances and bond angles from their nearest neighbor atoms have been determined. The substrates utilized in these investigations were low Miller Index surfaces of fee, hep and bcc metals in most cases, and low Miller Index surfaces of semiconductors that crystallize in the diamond, zincblende and wurtzite structures in some cases that could be cleaned and ordered with good reproducibility. 

Surfaces of real crystals never adopt the bulk-truncated structures shown in Fig. 4.5. They reconstruct or relax (inwards or outward movement of the atoms) to minimize their surface energy [42]. Known surface structures of zincblende and wurtzite structure semiconductors are summarized in [43]. Nonpolar surfaces of wurtzite (1120) and (1010) surfaces show no lateral surface reconstructions and are supposed to have a structure similar to the well-known zincblende (110) surface, which is characterized by an inward relaxation of the surface cations and partial electron transfer from the surface cation dangling bond to the surface anion dangling bond [42,43]. 

In the analyses of conventional zincblende (ZB) semiconductors, we frequently assume a parabolic band for the conduction bands, and the 6 x 6 Luttinger-Kohn Hamiltonians are used to describe the upper valence bands [1,2], In treating the valence bands together with the conduction bands on an equal footing, as when estimating the momentum matrix elements, we often make use of the 8 x 8 Kane Hamiltonian [3], However, the form of the Hamiltonians reflects the crystal symmetry, and Kane Hamiltonians are constructed under the condition of cubic symmetry. For wurtzite (WZ) materials, therefore, we must consider hexagonal symmetry in the effective Hamiltonian. Let us consider the 8 x 8 k.p Hamiltonian for WZ structure [4,5],... 

By introducing components along two axes, one sees that the corresponding susceptibility is the same for this model that is, Xn 22 = zWi 1 > though experimental values for zincblende-typc semiconductors give Zii 22 0-5 Zi 111 Wynne, 1969, Wang and Ressler, 1970, and Yablonovitch ct al., 1972). 

Sphalerite (or zincblende ) has a lattice with zinc atoms at the corners and face centers of a unit cube and sulfur atoms at the centers of four out of the eight smaller cubes into which the large cube can be divided. Both zinc and sulfur are in regular tetrahedral coordination. The cleavage surface is the (110) surface, and this nonpolar face of ZnS (and other zinc-blende-structure binary compounds) is by far the best understood of all semiconductor surfaces (Kahn, 1983). 

Oxides and sulfides with tetrahedrally coordinated cations such as those with the zincblende structure may undergo substantial surface reconstruction. There are consequently also substantial changes in electronic structure. Much of the work undertaken on surface characterization of oxides and sulfides has been concerned with materials of importance in semiconductors and catalysts, but a certain amount of work has also been prompted by the importance of surface studies in mineral technology. Examples include studies of the surface properties of chalcopyrite (Buckley and Woods, 1984), galena (Tossell and Vaughan, 1987), or pyrite during extraction by flotation (Brion et al., 1980). 

Pantelides, S., and W. A. Harrison (1975). Structure of the valence band of zincblende-type semiconductors. Phys. Rev. Bll, 3006-21. 

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

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. 

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