Inversion domain boundaries

A7.2 Planar defects in GaN basal plane faults, prismatic faults, stacking mismatch boundaries and inversion domain boundaries... 

Most wurtzite GaN films have been grown on either 6H-SiC(0001) (see Datareview A7.8) or sapphire (A1203) substrates. The orientation of sapphire most frequently used is C-plane (0001) although there have been some structural characterisation studies made for growth on A-plane (1120) [1-4] and R-plane (0112) [1,2,5-7] substrates. Other defects found in the a-phase include inversion domain boundaries, prismatic faults, nanopipes, pits, voids and cracks. The limited structural information available on bulk single crystals of a-GaN shows that they contain a low density of line dislocations and stacking faults near inclusions [12] (see Datareview A7.5). 

FIGURE 4 HREM image taken along the [1120] zone axis of an inversion domain (GaN ) in a GaN matrix. The inset is a simulation of the region near the inversion domain boundary with an overlay of the Ga (large circles) andN (small circles) atoms. (From [9].)... 

SiC terraces separated by a step. Unlike the case for sapphire, the polarity of the SiC 0001 surfaces and the bonding at the film/substrate interface prevents die formation of inversion domain boundaries (IDBs) in GaN grown on SiC 0001 [11,12,19]. Vermaut et al [10] identified the SMBs in GaN and AIN grown on SiC as prismatic stacking faults with three possible Burgers vectors / <2023>, V3 <10l0> and V2 <0001>. 

I ICP ICP-RIE ICTS ID IDB IR interstitial inductively coupled plasma etching inductively-coupled-plasma reactive ion etching isothermal capacitance transient spectroscopy inversion domain inversion domain boundary infrared... 

IC IDB IMPATT IR I-V integrated circuit inversion domain boundary impact ionization avalanche transient time infrared current-voltage... 

One of the particular features of m-plane GaN grown on m-plane SiG is the existence of the inversion domain boundaries. Each inversion domain is sxuTounded by the stacking faults as shown in Figure 5.9. Arrows in the figure shows the [0001] or +c direction. 

Figure 5.9 Inversion domain boundaries observed in plan view bright-held TEM image of the m-plane CaN grown on m-plane 4H-SiC with AlGaN/AIN interlayer.

Figure 15 Schematic representation of the oxygen-related defect evolution as a function of oxygen content (a) region I-isolated aluminum vacancy with associated oxygen, (b) region 11-aluminum octahe-drally coordinated to oxygen, and (c) extended defect-an inversion domain boundary consisting of aluminum atoms octahedraUy coordinated to oxygen at the boundary (26).

The dislocation density within the first 0.5 xm of the GaN film on the vicinal 6H-SiC(0001)si substrate was approximately 1x10 cm", as determined from initial plan view TEM analysis by counting the number of dislocations per unit area. This value is approximately an order of magnitude lower than that reported (43) for thicker GaN films deposited on sapphire(OOOl) substrates using low-temperature buffer layers. The dislocation density of the GaN film deposited on the vicinal 6H-SiC(0001)si substrate decreased rapidly as a function of thickness. In contrast, the on-axis wafers had less step and terrace features thus, the HT-AIN buffer layers on these substrates were of higher microstructural quality with smoother surfaces and fewer inversion domain boundaries. Consequently, the microstructural quality of the GaN films were better for on-axis growth as shown by the DCXRC data noted below. 

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