Of GaN film on sapphire

SUNG ETAL. Surface Structure of GaN Film on Sapphire... 

Aqueous processing, precursors for ferroelectric thin films, 95-104 Autocompensated surface structure of GaN film on sapphire experimental description, 26-27 experimental procedure classical ion trajectory simulations, 28 GaN sample, 27 first-layer species... 

A7.6 HRTEM characterisation of planar defects in GaN films on sapphire... 

Ning XJ, Chien FR, Pirouz P, Yang JW, Asif Khan M. Growth defects in GaN films on sapphire the probable origin of threading dislocations. J Mater Res 1996 11(3) 580. 

J. A. Freitas Jr and M. A. Khan, Raman and photoluminescence studies of undoped and magnesium-doped GaN films on sapphire , Mater. Res. Soc. Symp. Proc., 339, 547 (1994). 

Sputtered ZnO films were used to improve nucleation of GaN HVPE thick films on sapphire [2], It is not clear whether the ZnO is really a buffer layer or just a surfactant in this process. Subsequently, ZnO thin films were proposed as buffer layers for the growth of GaN by MBE [20], In practice, low-temperature AIN or GaN buffer layers have out-performed the ZnO-bufifer-layer approach... 

Preliminary measurements of terahertz emission from InN thin films deposited on GaN buffers on sapphire using fs... 

One of the major hurdles in the epitaxial growth of high quality GaN thin films is the unavailability of suitable substrates. The lack of suitable substrates leads to poor quality epitaxial films with dislocation densities in the range of 1010-1012 cm-2 for GaN grown on sapphire [1,2] and SiC [3]. Such high defect densities are detrimental to the device performance conventional III-V (like GaAs) devices have defect densities about four orders of magnitude lower than presently achievable in GaN. 

The in-plane polarization anisotropy can be enhanced by anisotropic strain. This can be achieved by choosing a nonpolar orientation with an appropriate substrate. In the extreme case of M-plane GaN on liAl02, the degree of linear polarization can be increased to its maximum value of one for all three transitions between the three uppermost valence bands (VBs) and the conduction band (CB), corresponding to complete linear polarization for all three transitions. This optical anisotropy can be observed in transmission (absorption) and reflection, as well as photoluminescence (PL) and photoreflectance (PR) spectroscopy. It can therefore be used for polarization filtering, polarization-sensitive photodetectors (PSPDs), and polarized light emitters. For anisotropically strained C-plane GaN films on (1120) sapphire, the in-plane polarization properties have been previously reported in Refs. 1-3. 

Figure 9.15 Experimental (dots) and calculated (solid lines) GIRSE spectra of a polar c-plane GaN film on a-plane sapphire for different angles between the plane of incidence and the GaN [1120] direction ...

Although first deposition experiments of nonpolar GaN films on r-plane sapphire were performed as early as in 1987 [5], the defect structure in wurtzite GaN and related compounds has been mainly studied in the past focusing on films oriented along the hexagonal [0001] axis (c-axis). Growth techniques such as molecular beam epitaxy (MBE) [1], metal organic vapor phase epitaxy (MOVPE) [6], and hydride vapor phase epitaxy (HVPE) [7,8] are established for polar as well as nonpolar GaN growth. The structural quality of a-plane GaN... 

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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