Residual Strain Evaluation by Cross-Sectional Micro-Reflectance Spectroscopy of Freestanding GaN Grown by Hydride Vapor Phase Epitaxy

Modulation of Electrical Conductivity and Lattice Distortions in Bulk HVPE-Grown GaN

“…The average Q values have been determined to Q as-grown = 4.8502 ± 0.0001 Å −1 and Q etched = 4.8493 ± 0.0006 Å −1 (c as-grown = 5.1818 ± 0.0001 Å and c etched = 5.1828 ± 0.0006 Å) which translates into a compressive strain of ɛ as-grown = −0.118% and ɛ etched = −0.101% with respect to the literature value of Q (004) = 4.8444 Å −1 (c (004) = 5.189 Å). 37 The presence of residual compressive stress in free standing HVPE grown bulk GaN substrates has been observed before by various techniques such as micro-reflectance spectroscopy, 38,39 HRXRD and photoluminescence spectroscopy. 40 However, the amount of residual compressive strain on the c-axis reported in these studies is significantly smaller (by one order of magnitude) compared to this work.…”

Growth and strain characterization of high quality GaN crystal by HVPE

“…To measure the residual strain, cross-sectional micro-reflectance measurements [11,12] were performed. Thin beam-like samples cleaved from the center of wafers were placed in a cryostat and cooled to 4 K using liquid He.…”

“…Details of the EPD for the r-FIELO and s-FIELO GaN crystals can be found in [11]. It should be noted that an EPD of a r-FIELO GaN film a few hundred micrometers thick was as low as 5 Â 10 6 cm À 2 .…”

“…Since exciton energies are highly sensitive to strain components, the depth profile of a very small residual strain can be detected by precisely measuring the excition energies at different positions. Details about the relationship between the strain components and exciton energies can be found in [11,12].…”

“…Details regarding the intrinsic strain can be found in [11]. As an approximation, the intrinsic strain for the freestanding FIELO GaN can be expressed as…”