Abstract:
A thick gallium nitride (GaN) film is formed on a LiAlO 2  substrate through two stages. First, GaN nanorods are formed on the LiAlO 2  substrate through chemical vapor deposition (CVD). Then the thick GaN film is formed through hydride vapor phase epitaxy (HVPE) by using the GaN nanorods as nucleus sites. In this way, a quantum confined stark effect (QCSE) becomes small and a problem of spreading lithium element into gaps in GaN on using the LiAlO 2  substrate is mended.

Description:
FIELD OF THE INVENTION 
     The present invention relates to growing GaN; more particularly, relates to growing a thick GaN film on a GaN nucleus sites through a chemical vapor deposition (CVD) and a hydride vapor phase epitaxy (HVPE). 
     DESCRIPTION OF THE RELATED ART 
     An environment for growing GaN through CVD and HVPE usually uses a lot of ammonia (NH 3 ) gas and hydrogen chloride (HCL) gas. And the HCl gas usually etches more surface than the NH 3  gas. 
     However, the growing procedure is complex and the GaN obtained is too thin. If GaN is grown directly under HVPE by using a LiAlO 2  substrate under a high temperature, a possible problem is that the lithium element in the substrate may be spread on a surface of the substrate before GaN nucleus sites are formed and thus a pollution may occur. 
     Consequently, the GaN obtained through the prior art may have HCl accumulated and lithium element spread into GaN structure, not to mention that the GaN obtained is too thin. Hence, the prior art does not fulfill all users&#39; requests on actual use. 
     SUMMARY OF THE INVENTION 
     The main purpose of the present invention is to grow GaN nanostructure through a CVD and growing a thick GaN film through a HVPE on the GaN nanostructure as nucleus sites. 
     Another purpose of the present invention is to effectively mend a problem of spreading lithium element into gaps in GaN while using a LiAlO 2  substrate. 
     To achieve the above purposes, the present invention is a method of growing GaN using CVD and HVPE, comprising steps of: (a) obtaining a LiAlO 2  substrate and a two-stage reactor device; (b) obtaining GaN nanorods through CVD in the reactor device under a high temperature; and (c) obtaining a thick GaN film through HVPE in the reactor device with the GaN nanorods as nucleus sites. Accordingly, a novel method of growing GaN using CVD and HVPE is obtained. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
       The present invention will be better understood from the following detailed description of the preferred embodiment according to the present invention, taken in conjunction with the accompanying drawings, in which 
         FIG. 1  is the flow view showing the preferred embodiment according to the present invention; 
         FIG. 2  is the view showing the LiAlO 2  substrate; 
         FIG. 3  is the view showing the GaN nanorods; and 
         FIG. 4  is the view showing the thick GaN film 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following description of the preferred embodiment is provided to understand the features and the structures of the present invention. 
     Please refer to  FIG. 1  to  FIG. 4 , which are a flow view showing a preferred embodiment; a view showing a LiAlO2 substrate; a view showing a GaN nanorods; and a view showing a thick GaN film according to the present invention. As shown in the figures, the present invention is a method of growing GaN using CVD and HVPE, comprising the following steps: 
     (a) Obtaining a LiAlO 2  substrate and a reactor device  11 : As shown in  FIG. 2 , a LiAlO 2  substrate  21  and a reactor device (not shown in the figures) are obtained. The substrate made of LiAlO 2  can be further a substrate made of sapphire (Al 2 O 3 ), lithium gallium oxide (LiGaO 2 ), lithium silicon oxide (Li 2 SiO 3 ), lithium germanium oxide (LiGeO 3 ), sodium aluminum oxide (NaAlO 2 ), sodium germanium oxide (Na 2 GeO 3 ), sodium silicon oxide (Na 2 SiO 3 ), lithium phosphor oxide (Li 3 PO 4 ), lithium arsenic oxide (Li 3 AsO 4 ), lithium vanadium oxide (Li 3 VO 4 ), lithium magnesium germanium oxide (Li 2 MgGeO 4 ), lithium zinc germanium oxide (Li 2 ZnGeO 4 ), lithium cadmium germanium oxide (Li 2 CdGeO 4 ), lithium magnesium silicon oxide (Li 2 MgSiO 4 ), lithium zinc silicon oxide (Li 2 ZnSiO 4 ), lithium cadmium silicon oxide (Li 2 CdSiO 4 ), sodium magnesium germanium oxide (Na 2 MgGeO 4 ), sodium zinc germanium oxide (Na 2 ZnGeO 4 ) or sodium zinc silicon oxide (Na 2 ZnSiO 4 ). The reactor device is a two-stage reactor device serially processing a CVD and an HVPE. 
     (b) Obtaining GaN nanorods through CVD  12 : As shown in  FIG. 3 , the LiAlO 2  substrate  21  deposed on a seat (not shown in the figure) is sent into the reactor device to be processed with the CVD. Under a high temperature, an ammonia (NH 3 ) gas and a gallium (Ga) metal are obtained as sources for nitrogen (N) element and Ga element. A N 2  gas is flowed as a carrying gas. The Ga metal is deposed in a movable boat. Then the NH 3  gas is directed in a quartz tube (not shown in the figures) to pass through a mass flow controller (not shown in the figures) for processing the CVD with a chemical reaction to obtain a GaN nanostructure of nanorods  211 . 
     (c) Obtaining a thick GaN film through HVPE  13 : As shown in  FIG. 4 , the LiAlO 2  substrate  21  having the GaN nanorods  211  is processed with the HVPE in the two-stage reactor device. A nitrogen gas is used as a diluent gas. The Ga metal and a HCl flowed into the two-stage reactor device are reacted under a temperature between 750 and 800 Celsius degrees (° C.) to obtain gallium chloride (GaCl). Then the GaN nanorods  211  are used as nucleus site where GaCl and NH 3  are mixed for reaction under a temperature between 500 and 600° C. to form a thin GaN film  212  on the LiAlO 2  substrate  21 . Then a temperature and a speed of the gases flowed in are adjusted for growing a thick GaN film. Thus, a novel method of growing GaN using CVD and HVPE is obtained. 
     On using the present invention, a Ga metal is put in a movable boat with a LiAlO 2  substrate  21  on a seat. The LiAlO 2  substrate  21  is processed with a CVD under a high temperature in a reactor device to grow GaN nanorods  211 . Therein, a linear boron nitride (BN) tube is used to prevent a quartz tube of the reactor device from pollution and to reduce an interfacial free energy between the GaN nanorods  211  and the LiAlO 2  substrate  21 . Thus, GaN nanorods  211  are obtained through the follow chemical formula:
 
2Ga+2NH 3 →2GaN+3H 2  
 
     Then the GaN nanorods  211  are used as nucleus sites to process the HVPE in the reactor device to directly grow GaN on the nucleus sites through the following formulas:
 
2Ga+2HCl←→2GaCl+H 2  
 
GaCl+NH 3 ←→GaN+HCl+H 2  
 
     And then the LiAlO 2  substrate  21  is transferred to a preheated place to be slowly cooled down in a room temperature. By adjusting a temperature of the LiAlO 2  substrate and by controlling a growing condition through a small temperature difference between the LiAlO 2  substrate  21  and its surrounding environment, a thick GaN film is finally obtained. And, owing to a weaker piezoelectric field of the two-stage reactor device, a quantum confined stark effect (QCSE) becomes smaller to effectively mend a problem of spreading lithium element into gaps in GaN while using a LiAlO 2  substrate. 
     To sum up, the present invention is a method of growing GaN using CVD and HVPE, where a CVD is used to grow a GaN nanostructure and then an HVPE is used to grow a thick GaN film on the GaN nanostructure as nucleus sites; and a problem of spreading lithium element into gaps in GaN while using a LiAlO 2  substrate is effectively mended. 
     The preferred embodiment herein disclosed is not intended to unnecessarily limit the scope of the invention. Therefore, simple modifications or variations belonging to the equivalent of the scope of the claims and the instructions disclosed herein for a patent are all within the scope of the present invention.