Epitaxial layers composition

Fig. 29. SIMS profiles of total deuterium density in two composite samples subjected to a one hour deuteration in the same plasma product environment at 300°C (Johnson, 1988). Both samples had a substrate containing 2 x 10IH Sb/cm3 this was covered with an epitaxial layer containing 3 x 1018 As/cm3 for the upper curve, and with one containing 5x 10 7 As/cm3 for the lower curve. There was in both cases a little interdiffusion. All sample surfaces were prepared for deuteration by removing the oxide with a dilute HF etch, rinsing with distilled water, and blowing dry with heated nitrogen.

Epitaxial Layers. Epitaxial deposition produces a single crystal layer on a substrate for device fabrication or a layer for multilevel conductive interconnects which may be of much higher quality than the substrate. The epitaxial layer may have a different dopant concentration as a result of introducing the dopant during the epitaxial growth process or may have a different composition than the substrate as in silicon on sapphire. Methods used for epitaxial growth include chemical vapor deposition (CVD), vapor phase epitaxy (VPE), liquid phase epitaxy (LPE), molecular beam epitaxy (MBE) and solid phase epitaxy (SPE). 

FIGURE 5 EDX composition analysis of GalnN on a GaN epitaxial layer for a thick GalnN layer with layer thickness of 2.0 pm. The open squares are the indium mole fractions of Region (I), and the closed circles are those of Region (II). 

Fig. 32. HREM image of a cross section prepared from a CdS epitaxial layer deposited on (111) InP with the same solution composition of Fig. 2 T = 60 °C. The arrows shows the interface between CdS and InP. (from [170]) With permission of Electrochem. Soc.

Solubility limits in solid solutions can be widened by annealing (tempering) a high-temperature phase or depositing a thin film of a solid solution on a substrate with the necessary structure (epitaxy). Thus, a single-crystal layer (50-60 nm) of the KCI0.5I0.5 composition (not known to exist as bulk mixed crystals), have been obtained on a KBr substrate at low temperature [98]. Solid solutions MgO-CaO of all concentrations were prepared as epitaxial layers on the MgO substrate at T=300 °C [99], their unit cell parameters conform to Vegard law. 

The formation and growth of an electrodeposited phase is a complex process and many methods have been used to study it. The main feature of our laboratory scientific investigations is intensive study of the structure of poly- and monocrystalline refractory metal deposits, such as tungsten, molybdenum, rhenium, iridium, ruthenium and etc. We have shown that the structure of electrodeposited layers directly depends on the conditions of electrolysis [1]. Moreover this structures a most sensitive instrument to study the properties of our electrolyte, including purity of the melt, ion composition, dissipative ability, and kinetic parameters of electrodeposition. It was established that the reduction of oxygen in a chloride melt changed the direction of molybdenum growth texture from <111> to <001 > direction with a fine structure of epitaxial layers [2]. 

The stracture shown in Fig. 3.73b is especially convenient for the application with Hgi xCdxTe epitaxial layers whose thickness is of the order of micrometers and whose composition x (and thus their bandgap) varies with the position within the sample, because the compositional nonuniformity can be used for additional decrease of the carrier concentration in the active part. 

Epitaxial layers of compound semiconductors are most frequently grown by chemical synthesis reactions. Thermodynamics can predict whether a reaction is feasible at all for the generation of crystalline solid from the vapor phase. It can, furthermore, predict the effect of variations in the experimentally controllable variables, such as input partial pressures and temperature on the yield of the reaction or the composition of solid solutions. 

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