Epitaxial layer

Chaimelling only requires a goniometer to inelude the effeet in the battery of MeV ion beam analysis teelmiques. It is not as eonnnonly used as tire eonventional baekseattering measurements beeause the lattiee loeation of implanted atoms and the aimealing eharaeteristies of ion implanted materials is now reasonably well established [18]. Chaimelling is used to analyse epitaxial layers, but even then transmission eleetron mieroseopy is used to eharaeterize the defeets. 

In a heterostRieture laser, the aetive region ean be defined by epitaxial layers and made eonsiderably thinner. In GaAs/Al Ga. As heterostRietures, the aetive region ean be made as thin as 100 nm, and the threshold euRent... 

Autodopiag occurs whea dopants are unintentionally released from a substrate through diffusion and evaporation, and subsequently reiacorporated during the deposition layer. Epitaxial layers are typically doped at concentrations of lO " -10 atoms/cm. The higher levels of doping are used in bipolar technology where the epilayer forms the transistor base. The epitaxial layer can be up to several hundred micrometers, and as thin as 0.05—0.5 p.m. Uniformities of 5% are common. 

A powerful feature of wet etching is the abiUty to achieve excellent etch selectivities of one material over another. This can be extremely useful in the fabrication of epitaxial devices with different material layers. Because selective etching allows the removal of specific layers, the final accuracy of the etch can approach that of the epitaxial layers. Etch selectivities of >100 1 have been achieved for citric acid H202 etching of GaAs—AlGaAs and InGaAs—InP stmctures (133). 

Arsenic from the decomposition of high purity arsine gas may be used to produce epitaxial layers of III—V compounds, such as Tn As, GaAs, AlAs, etc, and as an n-ty e dopant in the production of germanium and silicon semiconductor devices. A group of low melting glasses based on the use of high purity arsenic (24—27) were developed for semiconductor and infrared appHcations. 

Fig. 5. A gas manifold for the production of epitaxial layers of Group 111—V semiconductors by OMCVD where [...

For construction of suitable samples molecular beam epitaxy was selected, the method of choice for the production of complicated epitaxial layer systems with different materials. As substrates Si wafer material (about 20x20 mm-, thickness 1 mm) and SiO, discs (diameter 30 mm, thickness 3 mm) were used. Eight layered structures (one, two and three layers) were built up with Al, Co, and Ni, with an indicated thickness of 70 nm, each. 

Analysis of stress distributions in epitaxial layers In-situ characterization of dislocation motion in semiconductors Depth-resolved studies of defects in ion-implanted samples and of interface states in heterojunctions. 

Cathodoluminescence microscopy and spectroscopy techniques are powerful tools for analyzing the spatial uniformity of stresses in mismatched heterostructures, such as GaAs/Si and GaAs/InP. The stresses in such systems are due to the difference in thermal expansion coefficients between the epitaxial layer and the substrate. The presence of stress in the epitaxial layer leads to the modification of the band structure, and thus affects its electronic properties it also can cause the migration of dislocations, which may lead to the degradation of optoelectronic devices based on such mismatched heterostructures. This application employs low-temperature (preferably liquid-helium) CL microscopy and spectroscopy in conjunction with the known behavior of the optical transitions in the presence of stress to analyze the spatial uniformity of stress in GaAs epitaxial layers. This analysis can reveal,... 

Figure 4 Spatial variation of PL intensity of an InGaAsP epitaxial layer on a 2-in InP substrate shows results of nonoptimal growth conditions. (Data from a Waterloo Scientific SPM-200 PL mapper, courtesy of Bell Northern Research)...

A ZnSe-on-GaAs epitaxial layer required a sensitive survey of near-surface contamination. PAI was selected for ZnSe analysis because its major constituents and many of the expected impurities are elements that have poor ion yields in conventional LIMS. Figures 8 and 9 are two mass spectra acquired from the ZnSe epitaxial layer. 

RBS and channeling are extremely useful for characterization of epitaxial layers. An example is the analysis of a Sii-j Gejc/Si strained layer superlattice [3.131]. Four pairs of layers, each approximately 40 nm thick, were grown by MBE on a <100> Si substrate. Because of the lattice mismatch between Sii-jcGe c (x a 0.2) and Si, the Sii-j Ge c layers are strained. Figure 3.51 shows RBS spectra obtained in random and channeling directions. The four pairs of layers are clearly seen in both the Ge and Si... 

P. Ruggerone, C. Ratsch, M. Scheffler. In D. A. King, D. P. Woodruff, eds. Growth and Properties of Ultrathin Epitaxial Layers. Amsterdam Elsevier, 1997. 

J. C. Carrano, P. A. Grudowski, C. J. Biting, R. D. Dupuis, J. C. Campbell. Very low dark current metal-semiconductor-metal ultraviolet photodetectors fabricated on single-crystal GaN epitaxial layers. Appl Phys Lett 70 1992, 1997. 

The short penetration depth of UV/blue photons is the reason that frontside CCD detectors have very poor QE at the blue end of the spectrum. The frontside of a CCD is the side upon which the polysilicon wires that control charge collection and transfer are deposited. These wires are 0.25 to 0.5 /xm thick and will absorb all UV/blue photons before these photons reach the photosensitive volume of the CCD. For good UV/blue sensitivity, a silicon detector must allow the direct penetration of photons into the photosensitive volume. This is achieved by turning the CCD over and thinning the backside until the photosensitive region (the epitaxial layer) is exposed to incoming radiation. 

Other forces can arise as a result of elastic strain on the growing film, which can be due to a surface-induced ordering in the first few layers that reverts to the bulk liquid structure at larger distances. This elastic energy is stored in intermolecular distances and orientations that are stretched or compressed from the bulk values by the influence of the substrate at short distances [7]. Similar phenomena are well known to occur in the growth of epitaxial layers in metals and semiconductors. 

Various microstructures and configurations are possible for useful solid materials, including bulk single crystals and epitaxial layers, polycrystalline articles or thin films with controlled grain size (including micro- and nanocrystalline... 

A variety of compound semiconductors have been successfully prepared by this technique. Much of the work concerning ECALE has been concentrated on the deposition of CdTe on An substrates. Notwithstanding the inherent problems of the system (for instance, a 10% lattice mismatch), the formation of CdTe epitaxial layers became a model example of ECALE synthesis. In their pioneering studies, Stickney and co-workers [27, 28] have focused on the deposition of the compound on... 

Here, it is easy to see the various layers and steps necessary to form the IC. We have already emphasized the formation of the n- and p-wells 8uid the individual proeess steps needed for their formation. Note that an epitaxial layer is used in the above model. There are isolation barriers present which we have already discussed. However, once the polysilicon gate transistors are formed, then metal Interconnects must then be placed in proper position with proper electrical isolation. This is the function of the dielectric layers put into place as succeeding layers on the IC dice. Once this is done, then the wafer is tested. 

The mechanisms of the deposition process will be of crucial importance in determining the quality of the grown layers and when growth is optimal, with epitaxial layers grown, the process... 

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.

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