III- V semiconductors

Certain materials, most notably semiconductors, can be mechanically cleaved along a low-mdex crystal plane in situ in a UFIV chamber to produce an ordered surface without contamination. This is done using a sharp blade to slice tire sample along its preferred cleavage direction. For example. Si cleaves along the (111) plane, while III-V semiconductors cleave along the (110) plane. Note that the atomic structure of a cleaved surface is not necessarily the same as that of the same crystal face following treatment by IBA. 

Bruno G, Capezuttuto P and Losurdo M 1995 On the use of the piasma in iii-V semiconductor processing Phenomena In Ionized Gases (ICPIG Hoboken, NJ, 1995 (AiP Conference Proceedings voi 22) ed K FI Becker, W E Carr and E E Kunhardt (Woodbury, NY American Institute of Physics) pp 146-55... 

Fig. 6. Band gap versus lattice constant for Group 13—15 (III—V) semiconductors where (—) denotes direct gap and (-) iadirect. Liaes joining the...

As an example, PL can be used to precisely measure the alloy composition xof a number of direct-gap III-V semiconductor compounds such as Alj Gai j, Inj Gai jfAs, and GaAsjfPj j(, since the band gap is directly related to x. This is possible in extremely thin layers that would be difficult to measure by other techniques. A calibration curve of composition versus band gap is used for quantification. Cooling the sample to cryogenic temperatures can narrow the peaks and enhance the precision. A precision of 1 meV in bandgap peak position corresponds to a value of 0.001 for xin AljfGai j, which may be usefiil for comparative purposes even if it exceeds the accuracy of the x-versus-bandgap calibration. 

A useftil applicadon of time-dependent PL is the assessment of the quality of thin III-V semiconductor alloy layers and interfaces, such as those used in the fabri-cadon of diode lasers. For example, at room temperature, a diode laser made with high-quality materials may show a slow decay of the acdve region PL over several ns, whereas in low-quality materials nonradiative centers (e.g., oxygen) at die cladding interface can rapidly deplete the free-carder population, resulting in much shorter decay times. Measurements of lifetime are significandy less dependent on external condidons than is the PL intensity. 

Ph. Ebert, B. Engels, P. Richard, K. Schroeder, S. Bluegel, C. Domke, M. Heinrich, K. Urban. Contribution of surface resonances to scanning tunneling microscopy images (110) surfaces of III-V semiconductors. Phys Rev Lett 77 2997, 1996. 

The binary compounds of the Group 13 metals with the elements of Group 15 (N, P, As, Sb, Bi) are stmcturally less diverse than the chalcogenides just considered but they have achieved considerable technological application as III-V semiconductors isoelectronic with Si and Ge (cf. BN isoelectronic with C, p. 207). Their stmctures are summarized in Table 7.10 all adopt the cubic ZnS stmcture except the nitrides of Al, Ga and In which are probably more ionic (less covalent or metallic) than the others. Thallium does not form simple compounds... 

The III-V semiconductors can all be made by direct reaction of the elements at high temperature and under high pressure when necessary. Some properties of the Al compounds are in Table 7.11 from which it is clear that there are trends to lower mp and energy band-gap Eg with increasing atomic number. 

Compounds of As, Sb and Bi with the metals in Group 13 (Al, Ga, In, Tl) comprise the important III-V semiconductors whose structures, properties, and extensive applications have already been discussed (pp. 255-8). Group 14 elements also readily form compounds of which the following serve as examples GeAs mp 737°C, GeAsi mp 732°C, SnAs... 

The deposition temperature range is 250-600°C and the pressure is up to 20 T orr. T o minimize carbon inclusion, the carbonyl is highly diluted with hydrogen (ratio of 1/100) and high purity deposits can be obtained. PI Reaction (6) has a low temperature reaction and isbeing considered for deposition on silicon and III-V semiconductors. 

The lead compounds PbS, PbSe, PbTe are narrow-gap semiconductors that have been widely investigated for infrared detectors, diode lasers, and thermo-photovoltaic energy converters. Their photoconductive effect has been utilized in photoelectric cells, e.g., PbS in photographic exposure meters. Integrated photonic devices have been fabricated by their heteroepitaxial growth on Si or III-V semiconductors. 

Flat-Band Potentials and Positions of the Valence Band Maximum Evs and Conduction Band Minimum Ecs of Oxide Semiconductors, Group IV and III/V Semiconductors, and Mixed Oxide Semiconductors with Respect to the H+/H2 Scale, Where Minus Represents above Zero and Plus Represents below Zero... 

As a final comment on terminology, we note that elemental semiconductors are formed from a single element, e.g., Si or Ge, whereas compound semiconductors are formed from two binary), three ternary), four quaternary), or, rarely, more elements. Semiconductor alloys refer to solid solutions where either one anion or one cation can substitute for another, or possibly two or more such substitutions can occur for a binary semiconductor AB a simple alloy with C would be represented as Ai CjcB. Semiconductors are often classified by the group numbers in the periodic table. Thus, for example, I-VII semiconductors include Cul and AgBr, II-VI semiconductors include ZnS, CdTe, and HgTe, III-V semiconductors include GaAs, GaN, InP, and InSb, and IVx-VIv semiconductors include PbSe and Sn02. Fundamental physical properties are compiled in a recent handbook [22]. 

The ZB and WZ crystal structures are the most common types for binary octet semiconductors [23], and for III-V semiconductors they constitute practically the only ones known to occur. The energy differences between the two forms have been... 

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