GaN Crystals on Patterned and Non-Patterned Thin Film Substrates Grown by Na-Flux Method

doi:10.16553/j.cnki.issn1000-985x.2025.0218

Abstract

Abstract: In this study， GaN crystals were grown by Na-flux liquid-phase epitaxy method on patterned substrates （PS） and non-patterned substrates （NPS） at various growth temperatures. COMSOL numerical simulations were employed to calculate and analyze the nitrogen concentration distribution and supersaturation evolution in the Ga-Na melt under different temperature conditions. The combined experimental and simulation results systematically reveal the differences in epitaxial growth behaviors of GaN crystals on PS and NPS. The results indicate that epitaxial growth on PS was successfully achieved only at 840 and 850 ℃. The obtained GaN crystals exhibit a regular hexagonal pyramid morphology， with partially unfilled gaps observed in the upper region of the cross-sections. As the temperature increases from 840 ℃ to 850 ℃， the nitrogen concentration in the melt increases while the supersaturation decreases， leading to smoother pyramid facets and an increase in crystal thickness from approximately 570 μm to 810 μm. When the temperature raises to 860 ℃， the supersaturation decreases further， resulting in complete dissolution of the seed points and no epitaxial growth occurring. In contrast， stable epitaxial growth on NPS was achieved over the temperature range from 840 ℃ to 860 ℃. With increasing temperature， the surface morphology evolves from ridge-like structures at lower temperatures to flat， cell-like structures at higher temperatures， while the cross-sections exhibit dense and laterally continuous growth. The crystal thickness first increases and then decreases with temperature increasing， reaching a maximum of approximately 1 450 μm at 850 ℃. In addition， the thickness of the GaN crystals obtained on PS is significantly thinner than that on NPS. Overall， compared with NPS， PS has a narrower stable epitaxial growth window， which requires more precise control of growth parameters to achieve high-quality epitaxial crystal growth.

Key words: GaN crystal; Na-flux method; patterned substrate; non-patterned substrate; growth mode

CLC Number:

O782⁺.1

HUANG Gemeng, MA Ming, XIA Song, FAN Shiji, LI Zhenrong. GaN Crystals on Patterned and Non-Patterned Thin Film Substrates Grown by Na-Flux Method[J]. Journal of Synthetic Crystals, 2026, 55(3): 411-422.

Figures/Tables 15

Fig.1 Schematic diagram of PS substrate （a） and SEM image （b）

Table 1 Experimental process parameters

No.	Mass fraction of raw material/%			Temperature/℃	Pressure/MPa	Time/h	Substrate
No.	Ga	Na	C	Temperature/℃	Pressure/MPa	Time/h	Substrate
a-1	30	70	0.5	840	3.5	96	PS
a-2	30	70	0.5	840	3.5	96	NPS
b-1	30	70	0.5	850	3.5	96	PS
b-2	30	70	0.5	850	3.5	96	NPS
c-1	30	70	0.5	860	3.5	96	PS
c-2	30	70	0.5	860	3.5	96	NPS

Fig.2 Three-dimensional computational model of seed crystal placement

Table 2 Physical properties of Ga-Na melt

Parameter	Value
Density， ρ/（kg·m^-3）	2 100
Thermal conductivity， $k$ /（W·m^-1·K^-1）	16.01
Dynamic viscosity， μ/（kg·m^-1·s^-1）	3.99×10^-4
Thermal expansion coefficient， $β T$ /K^-1	2.65×10^-4

Table 2 Physical properties of Ga-Na melt

Parameter	Value
Density， ρ/（kg·m^-3）	2 100
Thermal conductivity， $k$ /（W·m^-1·K^-1）	16.01
Dynamic viscosity， μ/（kg·m^-1·s^-1）	3.99×10^-4
Thermal expansion coefficient， $β T$ /K^-1	2.65×10^-4

Fig.3 Optical images of GaN crystals epitaxially grown on different substrates at different temperatures

Fig.4 XRD patterns of GaN crystals epitaxially grown at different temperatures

Fig.5 Surface SEM images of GaN crystals epitaxially grown on different substrates at 840 and 850 ℃

Fig.6 Cross-sectional SEM images of GaN crystals epitaxially grown on different substrates at 840 and 850 ℃

Fig.7 Side SEM images of GaN crystals epitaxially grown on different substrates at different temperatures

Fig.8 SEM images of GaN crystal epitaxially grown on NPS at 860 ℃

Fig.9 Backside SEM images of GaN crystals epitaxially grown on PS at 840 and 850 ℃

Fig.10 Thickness of GaN crystals epitaxially grown on PS and NPS at different temperatures

Fig.11 Macroscopic nitrogen concentration distribution near the substrate surface at different temperatures

Fig.12 Distribution of GaN supersaturation near the substrate surface at different temperatures

Fig.13 Schematic diagram of GaN crystals epitaxially grown on different substrates

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