Comprehensive strain and band gap analysis of PA-MBE grown AlGaN/GaN heterostructures on sapphire with ultra thin buffer

Abstract

In this work, cluster tool (CT) Plasma Assisted Molecular Beam Epitaxy (PA-MBE) grown AlGaN/GaN heterostructure on c-plane (0 0 0 1) sapphire (Al2O3) were investigated by High Resolution X-ray Diffraction (HRXRD), Room Temperature Raman Spectroscopy (RTRS), and Room Temperature Photoluminescence (RTPL). The effects of strain and doping on GaN and AlGaN layers were investigated thoroughly. The out-of-plane (‘c’) and in-plane (‘a’) lattice parameters were measured from RTRS analysis and as well as reciprocal space mapping (RSM) from HRXRD scan of (002) and (105) plane. The in-plane (out-of plane) strain of the samples were found to be −2.5 × 10−3(1 × 10−3), and −1.7 × 10−3(2 × 10−3) in GaN layer and 5.1 × 10−3 (−3.3 × 10−3), and 8.8 × 10−3(−1.3 × 10−3) in AlGaN layer, respectively. In addition, the band structures of AlGaN/GaN interface were estimated by both theoretical (based on elastic theory) and experimental observations of the RTPL spectrum.

AlGaN Ultraviolet Metal–Semiconductor–Metal Photodetectors with Reduced Graphene Oxide Contacts

“…, where C AlN (4.9792 Å) and C GaN (5.1855 Å) are the bulk lattice constants of AlN and GaN, respectively, and δ c is the bowing parameter available from previous studies [20][21][22]. The Al mole fractions of the three samples were thus confirmed as 9.5%, 13.4%, and 17.9% (henceforth given in decimal form as 0.095, 0.134, and 0.179, respectively).…”

“…The lattice parameters (c) of the samples were calculated by the Bragg relation, = , where λ is the wavelength of the X-ray radiation used for the measurement, θB is the Bragg angle, and l is the Miller index. The Al mole fractions (x) of the samples were then calculated by Vegard's rule: 1855 Å) are the bulk lattice constants of AlN and GaN, respectively, and δc is the bowing parameter available from previous studies[20][21][22]. The Al mole fractions of the three samples were thus confirmed as 9.5%, 13.4%, and 17.9% (henceforth given in decimal form as 0.095, 0.134, and 0.179, respectively).…”

Impact of varying buffer thickness generated strain and threading dislocations on the formation of plasma assisted MBE grown ultra-thin AlGaN/GaN heterostructure on silicon

“…The in-plane biaxial stress in the GaN buffer can be expressed in terms of biaxial elastic modulus, M f as shown below (11) where, M f is expressed using the elastic constants c ij of GaN such as c 11 , c 12 , c 13 , c 33 .…”

“…In case of hexagonal GaN it is biaxial in nature. Measurement of in-plane biaxial stress in GaN buffer layer is performed using (11) and ((12)) which is displayed in the last column of Table III. Biaxial elastic modulus, M f in (12) can be calculated using the values of elastic constants c 11 = 390 GPa, c 12 = 145 GPa, c 13 = 106 GPa and c 33 = 398 GPa.…”

“…10 But in view of cost, scalability, thermal conductivity, high resistivity, silicon is the best contender as a replacement of all other substrates for supporting such coveted heterostructures, though it is a challenging approach to grow such thin barrier heterostructure on silicon substrate because of its lattice mismatch (∼17%) and thermal mismatch (∼54%) with GaN. 11 Overcoming these problems, use of silicon as a substrate for GaN growth is increasing 12,13 but for the formation of such ultra-thin AlGaN/GaN barrier-well region on silicon, needs critically optimized GaN buffer on silicon which should be of high quality. Crucial growth steps along with critical optimization of buffer thickness can only allow to grow high quality GaN that supports the formation of ultra-thin Al 0.2 Ga 0.8 N/GaN/Al 0.2 Ga 0.8 N barrier-well-barrier heterostructure on it.…”