Epitaxy liquid phase

Liquid phase epitaxy, or LPE, has been investigated in great detail because this was the first method for preparing monocrystalline garnet films for use as the ferrites in bubble computer memories, and more recently, for applications in magnetooptics. 

The term epitaxy is used to describe the growth of a monocrystalline film of one material in a definite crystallographic orientation on a crystal face of another material, the substrate. To promote growth, there must be a correspondence of both lattices at the interface. A misfit between film and substrate results in stresses as the film grows laterally, which may affect the stability of the deposited crystal. The magnetic properties of LPE garnet films can be optimised by varying this misfit. 

Substrates are non-magnetic solid solutions of rare-earth garnets with Ca , Mg and Zr ions. By varying the composition, almost any lattice parameter in the range 12.290-12.620 A can be obtained (Mateika, Laurien Rusche, 1982). 

To prepare a garnet film by LPE, a melt is obtained with the rare-earth (or Y) and Fe oxides in the appropriate proportions, in a PbO/BjOj flux, at typical temperatures of 970-1100 °C, Fig. 3.22. A small excess of FcjOs is added to maintain the composition within the Fe203-[Pb0/B203]-Y3Fe50j2 triangle, with the garnet as the primary phase field. A large supercooled state (10-40 °C) can be produced in the melt the substrate is placed just above the melt surface for a few minutes to ensure that its temperature is the same as that of the melt it is then 

Single-crystal spinel ferrite films can be epitaxially grown on MgO substrates. The ferrite, in a melt with Na2C03 as solvent, is deposited on the substrate at temperatures of 1100-1250 °C. Crystallisation of the 

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LPE = liquid-phase epitaxy, MOCVD = metalorganic chemical vapor deposition, VPE = vapor-phase epitaxy. 

The composition must be controlled to give the required emission wavelength. Techniques utilized include molecular-beam epitaxy (MBE) and liquid-phase epitaxy (LPE). 

Boats and crucibles for liquid phase epitaxy. Crucibles for molecular beam epitaxy. 

Most of these compounds were originally prepared by liquid-phase epitaxy. That process is now largely replaced by MOCVD, particularly in the case of gallium arsenide, gallium arsenic phosphide, and gallium aluminum phosphide. 

Figure 12.16b shows the a typical cross-section through a GaAsPLED fabricated from layers grown by either liquid phase epitaxy or vapor phase epitaxy. 

These processes can also involve reactants in the liquid phase, and we call this liquid-phase epitaxy, although the equations wiU be the same as for gases. 

Figure 4.9. Scanning electron microscope photographs showing the roughening transition of 111) faces of a TiOj crystal and the formation of hollowed needle crystals as impurities are added [19]. Growth occurs by liquid phase epitaxy on a (001) substrate. Fe203 is added as an impurity in the following amounts (a) 0%. (b) 1.3 mol%,...

Figure 19.1 Device for liquid phase epitaxial growth of several layers.

Vapor-phase deposition of the sputtered or evaporated layer-forming material avoids the undercooling problems associated with liquid phase epitaxy, but it coats everything in the vaporization chamber unselectively. Sputtering is usually done by forming a plasma (ionized gas) in an electrical discharge in the vapor at low pressure. 

Fig. 4. Energy below the conduction band of levels reported in the literature for GaP. States are arranged from top to bottom chronologically, then by author. At the left is an indication of the method of sample growth or preparation liquid phase epitaxy (LPE), liquid encapsulated Czochralski (LEC), irradiated with 1-MeV electrons (1-MeV e), and vapor phase epitaxy (VPE). Next to this the experimental method is listed photoluminescence (PL), photoluminescence decay time (PLD), junction photocurrent (PCUR), photocapacitance (PCAP), transient capacitance (TCAP), thermally stimulated current (TSC), transient junction dark current (TC), deep level transient spectroscopy (DLTS), photoconductivity (PC), and optical absorption (OA).

Fig. 3.38 Carrier concentration p versus pressure of As gas P for the crystals obtained by reheating undoped n-GaAs, which was prepared by the method of liquid phase epitaxy (LPE) at 850 °C. ...

A similar experiment was performed on the crystals grown by the method of liquid phase epitaxy (LPE) as the starting crystal. The starting crystals were reheated under various pressures of As gas at 850 °C for 30 min. Figure 3.38 shows the hole concentration, p, dependence on Pas at the surface of the heat-treated crystals. (The starting crystals showed n-type conduction, and after heat-treatment under this condition, only 7 pm of the surface of... 

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