Anisotropically Biaxial Strain in a-Plane AlGaN on GaN Grown on r-Plane Sapphire

Abstract

In this study, the anisotropically biaxial strain in a-plane AlGaN on GaN is investigated by X-ray diffraction (XRD) analysis using an AlGaN/GaN heterostructure grown on r-plane sapphire. In accordance with XRD reciprocal lattice space mapping, when the AlN molar fraction x in the AlGaN layer is 0.18, the AlGaN layer is fully strained under tensile stress and grows coherently on the underlying GaN layer. However, when x is as large as 0.31, partial relaxation is observed only in the c-axis direction. The tensile stress in the AlGaN layer is calculated taking the actual in-plane lattice constants of the underlying GaN layer into account, and it was found that the stress in the a-plane AlGaN layer in the c-axis direction is approximately 1.7 times larger than that in the m-axis direction.

Growth and investigation of m-plane (In)GaN buffer layers on LiAlO2 substrates

“…In [4,13]. In contrast to that, the sample with the thickest InGaN:Mg layer features an In fraction of 7.6% and strain values of -0.5% and 0.1% for the [11][12][13][14][15][16][17][18][19][20] and [0001] direction, respectively, indicating a relaxation of the GaN film. The InGaN:Mg film is also strained and exhibits a slight shift to lower angles with rising In content in (2-200) 2Θ/ω scans (not shown here).…”

“…Phase purity and crystal quality of the m-plane GaN were attested by high resolution X-ray diffraction (HRXRD) using a PANalytical Material Research Diffractometer and software analysis tool. The evaluation of strain and indium fraction was performed using methods and elastic constants given in [11]. Atomic force microscopy (AFM) scans were performed to measure the surface roughness.…”

“…As a second advantage, nonpolar light emitters exhibit a much lower wavelength shift with higher driving currents due to the absence of polarization field screening normally occurring in c-plane GaN [2]. One interesting approach to achieve this is to grow on (100) LiAlO 2 substrates, which enables a deposition of GaN in m-plane orientation with a rather small substrate-lattice mismatch of only 1.7 % and 0.3 % in [11][12][13][14][15][16][17][18][19][20] and [0001] direction of GaN, respectively [3]. The substrates can be manufactured by conventional Czochralski pulling method which allows potentially cheap large-size wafer production.…”

Growth and characterization of green GaInN-based light emitting diodes on free-standing non-polar GaN templates

“…This d-spacing averages the properties of the GaInN well and the GaN barrier as follows: Assuming that the shear stress does not exist in such non-polar crystalline system per linear elastic theory [9], Tsuda et al derived a simplified expression for stress and strain as given in Ref. [10]. Since the epitaxial layers are free to expand or contract in the growth direction, the stress along this direction vanishes.…”

a ‐plane AlN and AlGaN growth on r ‐plane sapphire by MOVPE

“…In recent years, intense research on nonpolar AlN and AlGaN has been performed with the aim of application to LEDs and LDs in the deep ultra-violet (UV) region [1][2][3][4]. However, while LEDs based on c-plane AlN with a wavelength of 210 nm have been commercially realized [5], in the case of LEDs using nonpolar AlN, only wavelengths of up to 363 nm have been reported [6].…”