Sapphire substrates

TABLE 6 Values of thermal expansion coefficient (TEC) for AIN, GaN and InN, together with the values for the most popular substrates sapphire, SiC and LiGaOi. 

Alumina films are used for surface coatings on carbide tools, as dielectric layers in transistor fabrication, as matched substrates (sapphire) for the growth of optically active materials such as gallium nitride, and as coatings for optical components. 

Figure C2.16.2 shows tire gap-lattice constant plots for tire III-V nitrides. These compounds can have eitlier tire WTirtzite or zincblende stmctures, witli tire wurtzite polytype having tire most interesting device applications. The large gaps of tliese materials make tliem particularly useful in tire preparation of LEDs and diode lasers emitting in tire blue part of tire visible spectmm. Unlike tire smaller-gap III-V compounds illustrated in figure C2.16.3 single crystals of tire nitride binaries of AIN, GaN and InN can be prepared only in very small sizes, too small for epitaxial growtli of device stmctures. Substrate materials such as sapphire and SiC are used instead.

Thermal—Oxidative-Resistance Coatings. The thermal stabihty of coatings produced by either covalendy or noncovalendy incorporating 2,4-dinitroaniline into an inorganic siUcate network and coating it onto a sapphire substrate has been examined (67). Although some increase in the thermal... 

At the end of last century, a near frictionless carbon (NFC) coating was reported, which is practically hydrogen contained DLC film grown on steel and sapphire substrates using a plasma enhanced chemical vapor deposition (PECVD) system [50]. By using a ball on a disk tribo-meter, a super low friction coefficient of 0.001-0.003 between the films coated on both the ball and the disk was achieved [50]. A mechanistic model was proposed that carbon atoms on the surface are partially di-hydrogenated, resulting in the chemical inertness of the surface. Consequently, adhesive interaction becomes weak and super low friction is achieved [22],... 

One method we might use is to cool the melt to incipient nuclei-formatlon. toss in the seed-crystal, and allow the melt to freeze into a single crystal. This is the KYROPOULOS method which we will discuss in detail later. Alas, this method only works for a few systems, notably alkali halides (cubic) and the like. We find that we can use a seed-crystal to grow single crystals, but only if we use it under carefully defined conditions. A modified K5rropoulos method has been used for many years to form single-crystal sapphire up to 13.0 inches in dieimeter. Plates cut from such crystals are used as windows and substrates for all sorts of integrated circuits, as well as watch "crystals". 

CdS Low-pressure MOCVD (10-2 torr), He and H2 carrier gas, Si02, A1203, sapphire, (lll)Si and (lll)InP substrates, growth temperatures >450 °C, polycrystalline films, gave mixture of hexagonal and cubic phase on Si02 substrate 183... 

N3)2Ga N(CH2CH2NEt2)2 ] low volatility Horizontal hot-wall LP-CVD Growth temperature 750-950 °C, preferred orientation of crystallites perpendicular to c-plane of sapphire substrate, no additional N source 287... 

Cl2Ga(N3)] air sensitive, sublimes at 70-100 °C in vacuum UHV-CVD Heteroepitaxial growth on Si and sapphire substrates at 650-700 °C, 1 1 films, no need for additional N source 293... 

Cl2Ga(N3)(NMe3) Cold-wall CVD 1 1 GaN grown at 700 °C on Si and sapphire substrates, chlorine and carbon contamination 293... 

In 1987, Swartz [73] measured the thermal boundary resistance between metal films and the dielectric substrates onto which the films were deposited, in the range 0.6-200 K. A typical example is the measurement of the thermal contact resistance between indium and sapphire [72]. To minimize the dependence on surface irregularities, indium was vacuum deposited onto the sapphire rods the two surfaces were then pressed together and annealed. Analogous measurements have been carried out also with lead and aluminium. In all these cases, it has been clear that the contact resistance was strongly dependent on the sample preparation. In particular, obtained data suggest that the contact between the two materials was not complete. 

GaN as a semi-conducting material for electronics is about to be launched on the market, especially for the use in blue- and UV-emitting LEDs and laser diodes [2]. The material is deposited on crystalline substrates like sapphire using thin-film epitactical techniques. Often, metal-organic chemical vapor deposition (MOCVD) is used. The necessity for such technologies limits the production rate and pushes up costs. 

Fig. 12.7 InGaAsP/InP multi quantum well semiconductor structure process (a) Si02 etch mask deposition (b) PMMA spin coating (c) E beam lithography and develop (d) Si02 etch (e) PMMA stripping (f) InGaAsP membrane etch (g) Si02 stripping (h) Chip flipping and bonding to sapphire (i) InP substrate etch (j) Adhesive etch...

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