Effect of High-temperature Annealing on AlN Crystal Grown by PVT Method

doi:10.15541/jim20220481

Abstract

Abstract:

In the process of PVT growth of AlN crystals, there is difficult to maintain ideal thermodynamic equilibrium conditions, causing crystal defects being inevitably generated. High temperature annealing technology has received much attention due to their effectiveness in improving crystal integrity. In this paper, AlN samples grown by PVT method were annealed at high temperature in N₂ atmosphere. In order to evaluate the crystalline quality and structural perfection of AlN before and after thermal annealing, high-resolution X-ray diffraction (HRXRD) and Raman spectrum were carried out. In addition, the impurity related band gap changes in the optical properties of AlN crystals were characterized by room temperature photoluminescence (PL) and absorption spectra. The crystal quality of these AlN crystals was significantly improved after annealing at 1400-1800 ℃. The full width at half maximum (FWHM) of the (10¯12) plane X-ray rocking curve decreased from 104.04 to 79.92 arcsec (1 arcsec=0.01592°) after annealing at 1400 ℃. As the annealing temperature increases, the absorption was significantly enhanced and the band gap became larger, indicating that the annealing process was beneficial to improve the quality of AlN crystals. The results of secondary ion mass spectrometry (SIMS) demonstrate that the annealing process reduces the C impurity, resulting in an increase in band gap of AlN crystal, which is consistent with the results of optical absorption.

Key words: high temperature annealing technology, AlN crystal, C impurities, bandgap

CLC Number:

TB34

YU Ruixian, WANG Guodong, WANG Shouzhi, HU Xiaobo, XU Xiangang, ZHANG Lei. Effect of High-temperature Annealing on AlN Crystal Grown by PVT Method[J]. Journal of Inorganic Materials, 2023, 38(3): 343-349.

Figures/Tables 8

Fig. 1 Photos of AlN crystal sample (a) Bulk AlN crystal; (b) Polished AlN crystal

Fig. 2 Schematic view of high temperature annealing process (a) High temperature annealing furnace; (b) High temperature annealing process

Fig. 3 EBSD of AlN crystal sample (a) EBSD Kikuchi patterns of AlN crystal without annealing; (b) Band slop obtained from EBSD mapping date; (c) Pole figures of AlN without annealing

Fig. 4 XRD ω-scan rocking curves of AlN (10¯12) diffractions

Table 1 Calculated edge dislocations density(ρe) of AlN samples

Sample	(10¯12) FWHM/arcsec^*	Edge dislocations density, ρ_e/(×10⁷, cm^-2)
Raw	104.04	5.80
AlN-1400	79.92	3.42
AlN-1600	78.92	3.34
AlN-1800	97.2	5.06

Fig. 5 Raman spectra of AlN samples without and with annealing at different temperatures

Fig. 6 Optical absorption spectra of the AlN crystals with and without annealing (a) Absorption spectra of the AlN without and with annealing at different temperatures with right enlarged spectra showing an absorption peak at 634 nm; (b) Correlation curves of (αE)2 on E with inset showing the band gap of AlN without and with annealing at different temperatures

Fig. 7 SIMS depth profiles of AlN crystal without (a) and with annealing at 1600 ℃ (b)

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