Sapphire Substrates for Growth of GaN and Related Compounds

In this Datareview, properties of sapphire as the substrate for growth of group III nitrides are described. Since sapphire substrates commercially available are exclusively a-sapphire, sapphire here is a-sapphire. 

Bulk physical properties of a-sapphire are listed in TABLE 1. The crystal structure is corundum type and quite often represented by hexagonal cell vectors. The atom arrangement of sapphire is shown in FIGURE 1. Sapphire is composed of Al3+ and O2 ions. The Al3+ ions occupy 2/3 of the octahedral sites and the O2 ions form a hexagonal close-packed (HCP) structure [11]. The origin of coordinates is taken at an Al-vacancy [11], The lattice constants are a = 0.4758 nm and c = 1.299 nm at 25°C [12], The Bragg condition for the c-plane (0001) is satisfied at 1 = 6m (m is an integer) and thus the plane distance for 1 = 6 is d = c/6 = 0.2165 nm. AIN and GaN have lattice constants c = 0.498 nm and 0.519 nm, respectively, and the plane distances for 1 = 2 are 0.249 nm and 0.2595 nm, respectively 

Crystal structure Density Lattice constants Thermal conductivity 

Melting point Specific heat Hardness Bulk modulus Elastic constants 

FIGURE 1 Crystal structure of a-sapphire. Hexagonal cell vectors are commonly used to represent the structure. 

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B2.1 Sapphire substrates for growth of GaN and related compounds TABLE 1 Bulk physical properties of a-sapphire [7,12,15,16,18],... 

B2.1 Sapphire substrates for growth of GaN and related compounds D SUMMARY... 

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