Progress in GaN Single Crystals: HVPE Growth and Doping

doi:10.15541/jim20220607

Abstract

Abstract:

Compared with the first and second generation semiconductor materials, the third generation semiconductor materials exhibit higher breakdown field strength, higher saturated electron drift velocity, outstanding thermal conductivity, and wider band gap, suitable for manufacturing of electronic devices with high frequency, high power, radiation resistance, corrosion resistant properties, optoelectronic devices and light emitting devices. As one of the representatives of the third generation of semiconductor materials, gallium nitride (GaN) is an ideal substrate material for preparing blue-green laser, radio frequency (RF) microwave and power electronic devices. It has broad application prospects in laser display, 5G communication, phased array radar, aerospace, etc. Hydride vapor phase epitaxy (HVPE) method is the most promising method for growth of GaN crystals due to its simple growth equipment, mild growth conditions and fast growth rate. Due to the widely used quartz reactors, unintentionally doped GaN obtained by HVPE method inevitably has donor impurities (Si and O). Therefore, the grown GaN shows n-type electrical properties, high carrier concentration and low conductivity, which limits its application in high-frequency and high-power devices. Currently, doping is the most common method to improve the electrical performance of semiconductor materials, through which different types of GaN single crystal substrates can be obtained with different dopants to improve their electrochemical characteristics and meet the different needs of market applications. In this article, the basic structure and properties of GaN semiconductor crystal material are introduced, and the recent progress of the high quality GaN crystals grown by HVPE method is reviewed; and the doping characteristics, dopant types, growth process and the influence of doped atoms on the electrical properties of GaN are introduced. Finally, the challenges and opportunities faced by the HVPE method to grow doped GaN crystals are briefly described, and the future developments in several directions are prospected.

Key words: gallium nitride, hydride vapor phase epitaxy, doping, crystal growth, review

CLC Number:

TB34

QI Zhanguo, LIU Lei, WANG Shouzhi, WANG Guogong, YU Jiaoxian, WANG Zhongxin, DUAN Xiulan, XU Xiangang, ZHANG Lei. Progress in GaN Single Crystals: HVPE Growth and Doping[J]. Journal of Inorganic Materials, 2023, 38(3): 243-255.

Figures/Tables 10

Fig. 1 Schematic diagram of GaN[4] (a) Hexagonal unit call (left) and the bond structure of GaN (right), with green balls indicating Ga atoms and blue balls indicating N atoms; (b) Polar face (left), non-polar face (middle) and one kind of semi-polar faces (right) of GaN crystal

Fig. 2 Structure of HVPE reactor[8]

Fig. 3 Photos and characterization of GaN crystals grown by HVPE (a) 2-inch 2.5 mm thick GaN crystal; (b) (0002) surface high-resolution XRD pattern; (c) (10¯12) high-resolution XRD pattern; (d) Image of GaN wafers; (e) CL image (dislocation density ~5×106 cm-2); (f) AFM image (RMS<0.2 nm in the range of 10 μm×10 μm)

Table 1 Different types of doped GaN[2-3,32]

Type	Impurities	Dopant	Characteristic	Application	Ref.
n type	Si	SiCl₂H₂	High carrier concentration; anti-surfactant effect	High power and high current optoelectronic devices (LED, LD)
n type	Ge	GeCl₄/Ge₃N₄	Little effect on lattice structure and stress, causing no morphological deterioration, higher carriers concentration than that of Si-doped; creating cavities inside the sample		[3]
p type	Mg	Mg(S)	Increased lattice constant and band gap width, high conductivity	Luminescent device	[32]
Semi- insulating	Fe	Fe(S)/Cp₂Fe	High resistivity (iron showing a parasitic effect, easy to diffuse)	High power/frequency devices, HEMT, photoconductive switch, detectors	[2]
	Mn	Mn(S)
	C	CH₄/C₂H₄/C₅H₁₂

Fig. 4 Si-doped HVPE-GaN[38] (a) Structure of Si-doped HVPE-GaN reactor; (b) Image of 800 μm- thick Si-doped HVPE-GaN; (c) Distribution of free carrier concentration along the diameter of Si-doped HVPE-GaN

Fig. 5 Ge-doped HVPE-GaN[47] (a) Structure of Ge-doped HVPE-GaN reactor; (b) Morphologies of Ge-doped HVPE-GaN: crystallized in H2 carrier gas (left), crystallized in N2 carrier gas (middle), distribution of free carrier concentration along the diameter of Ge-doped HVPE-GaN

Fig. 6 Mg-doped HVPE-Ga (a) Schematic of the HVPE system for growth of Mg doped GaN using MgO[53]; (b) Hole concentration measured at room temperature as a function of Mg concentration[55]; (c) Compensating donor concentration (Nd) and acceptor concentration (Na) as a function of Mg concentration[55]

Fig. 7 Image of semi-insulated GaN wafers (a) Fe-doped[62]; (c) Mn-doped[63]; (b) C-doped[60]

Fig. 8 Fe-doped GaN (a) Resistivity as a function of reciprocal temperature for samples doped with Mn, C, and Fe[8]; (b) Formation energy versus Fermi level for FeGa, FeN and Fei in GaN in different charge states, under Ga-rich conditions[68]; (c) Carrier concentration and Hall mobility versus Fe concentration in GaN films co-doped with Si and Fe[70]; (d) Resistivity versus inverse temperature for samples doped with Fe at various Fe concentrations[63]; (e) Schematic diagram of the energy levels and carrier decay processes of Fe-doped GaN[71]; (f) Carrier trapping time for Fe-doped GaN bulk crystals[72]

Fig. 9 C-doped GaN (a) Formation energy versus Fermi level for CGa and CN in GaN: Ga-rich conditions (left), and N-rich conditions (right)[79]; (b) CN impurity model in GaN[79]; (c) Optical transitions of CN in GaN[79]; (d) Defect density as a function of C concentration[81]; (e) Temperature-dependent resistivity for C doped GaN[82] ; (f) Concentrations of carbon, oxygen, and silicon in C-doped GaN layers versus the input mole fraction of pentane[82]

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