Abstract:
A method of growing nitride semiconductor material and particularly a method of growing Indium nitride is disclosed can increase surface flatness of a nitride semiconductor material and decrease density of V-defects therein. Further, the method can increase light emission efficiency of a quantum well or quantum dots of the produced LED as well as greatly increase yield. The method is also applicable to the fabrications of electronic devices made of nitride semiconductor material and diodes of high breakdown voltage for rectification. The method can greatly increase surface flatness of semiconductor material for HBT, thereby increasing quality of the produced semiconductor devices.

Description:
BACKGROUND OF THE INVENTION 
   The application claims priority to a Taiwan application No. 096148945 filed Dec. 20, 2007. 
   1. Field of Invention 
   The invention relates to methods of growing nitride semiconductor material and more particularly to such a method of growing nitride semiconductor material with improved characteristics including increased flatness and decreased density of V-defects, thereby increasing yield and increasing light emission efficiency of LEDs (light-emitting diodes) made of a material including the nitride semiconductor material. 
   2. Description of Related Art 
   The rapid advances in light-emitting diodes (LEDs) have led to the advent of the solid-state lighting era for reduced consumption of natural resources. InGaN alloy is the most promising material for high-efficiency light sources because of its direct band gap nature and widely spanned emission spectrum from ultraviolet to infrared. Moreover, the excellent properties of GaN-based materials such as high temperature stability, high breakdown voltage, high electron velocity, strong piezoelectric effect and high current density let the GaN high electron mobility transistor (HEMTs), Schottky diodes, and hetero-junction bipolar transistors (HBTs) are a good candidate for the applications of high speed and high power. 
   However, the external quantum efficiencies (EQE) of InGaN green LEDs still falls short of what is required. Poor internal quantum efficiency has been identified to be the bottleneck and has become the focus of intensive studies recently. The fundamental issue of this task is to obtain high quality In x Ga 1-x N alloys at a high indium mole fraction, which often leads to low crystalline quality due to indium aggregation and/or phase separation. Furthermore, V-defects are the most common defect that occurs at InGaN/GaN quantum wells of high indium mole fraction. Previous works have demonstrated that the V-shape defects are easily formed in high indium MQW, not only from buffer layer treading dislocations, but also within the MQW because of strain relaxation associated with stacking faults or indium segregation. It is possible of increasing light emission efficiency of LEDs and increasing yield by increasing flatness and decreasing density of V-defects. Thus, it is desirable to provide a novel method of growing nitride semiconductor material. 
   SUMMARY OF THE INVENTION 
   It is therefore one object of the invention to provide a method of growing nitride semiconductor material for a plurality of semiconductor devices, the method comprising flowing Triethyl-gallium (TEGa) and ammonia (NH 3 ) into a chamber to grow a first barrier layer; flowing Trimethyl-indium (TMIn) into the chamber to grow a first well layer; stopping flowing TEGa to grow an InN treatment layer in the chamber; stopping flowing TMIn; flowing TEGa into the chamber to grow a second barrier layer; and forming an InN-based LED of multiquantum well (MQW). The method can be applied to the manufacturing of InN MQW LED, InN quantum dots LED structure, rectifier, HBT, or HEMT. By utilizing this method, advantages including increased flatness, decreased density of V-defects, increased yield and increased light emission efficiency of LEDs made of a material including the nitride semiconductor material can be obtained. 
   The above and other objects, features and advantages of the invention will become apparent from the following detailed description taken with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a graph showing multiquantum well (MQW) growth direction versus different flows for InN treatment active layer manufactured according to a method of the invention; 
       FIG. 2  is a sectional view showing the constituent layers of an InN MQW LED structure manufactured according to the method of the invention; 
       FIG. 3  is a sectional view showing the constituent layers of the InN treatment active layer of  FIG. 2 ; 
       FIG. 4  is an atomic force microscopy (AFM) photograph showing Y direction versus X direction for samples (a), (b), (c) and (d) utilized in the invention; 
       FIG. 5  plots integrated PL intensity versus temperature for the sample (c) having an MQW without TMIn treatment and the sample (d) having an MQW with TMIn treatment; 
       FIG. 6  plots output power versus current for the sample (e) showing an LED structure without TMIn treatment and the sample (f) showing an LED structure with TMIn treatment; 
       FIG. 7  is a transmission electron microscopy (TEM) photograph showing a quantum well (a) with TMIn treatment and a quantum well (b) without TMIn treatment according to the invention; 
       FIG. 8  is a sectional view showing the constituent layers of InN quantum dots LED structure manufactured according to the method of the invention; 
       FIG. 9  is a sectional view showing the constituent layers of a HBT structure manufactured according to the method of the invention; 
       FIG. 10  is a sectional view showing the constituent layers of a HEMT structure manufactured according to the method of the invention; and 
       FIG. 11  is a sectional view showing the constituent layers of a rectifier structure manufactured according to the method of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , it is a graph showing multiquantum well (MQW) growth direction versus different flows for InN treatment active layer  100  manufactured according to a method of growing nitride semiconductor material of the invention. The method comprises the following steps. 
   First, flow Triethyl-gallium (TEGa) and ammonia (NH 3 ) into a chamber to grow a first barrier layer  101 A. 
   Next, flow Trimethyl-indium (TMIn) into the same chamber to grow a first well layer  101 B. 
   Next, stop flowing TEGa to grow an InN treatment layer  101 C in the chamber. Next, stop flowing TMIn and flow TEGa into the chamber again to grow a second barrier layer  102 A. 
   Finally, an InN treatment LED of MQW is produced. The LED has a flat MQW structure with decreased density of V-defects and increased light emission efficiency. 
   Referring to  FIG. 2 , it is a sectional view showing the constituent layers of an InN treatment MQW LED structure  200  manufactured according to the method of the invention. From bottom to top, there are grown of the following components. A sapphire substrate  210  is on the bottom. A gallium nitride (GaN) un-doped buffer layer  220  is deposited on the sapphire substrate  210  by growing. A GaN doped silicon N-type contact layer  230  is deposited on the GaN un-doped buffer layer  220  by growing. A GaN un-doped N-type layer  240  is deposited on the GaN doped silicon N-type contact layer  230  by growing. An InGaN/GaN MQW active layer  250  is deposited on the GaN un-doped N-type layer  240  by growing. An AlGaN magnesium electron blocking layer  260  is deposited on the InGaN/GaN MQW active layer  250  by growing. Finally, a GaN doped magnesium P-type contact layer  270  is deposited on the AlGaN magnesium electron blocking layer  260  by growing. 
   Referring to  FIG. 3 , it is a sectional view showing the constituent layers of the InGaN/GaN MQW active layer  250 . The InGaN/GaN MQW active layer  250  comprises, from bottom to top, the following components. 
   First, a first barrier layer  251 A is grown. Next, a first well layer  251 B is deposited on the first barrier layer  251 A by growing. Next, flow TMIn and NH 3  into the chamber to grow a first InN treatment layer  251 C on the first well layer  251 B. 
   Thereafter, a second barrier layer  252 A is deposited on the first InN treatment layer  251 C by growing. Next, a second well layer  252 B is deposited on the second barrier layer  252 A by growing. Next, flow TMIn and NH 3  into the chamber to grow a second InN treatment layer  252 C on the second well layer  252 B. 
   Thereafter, a third barrier layer  253 A is deposited on the second InN treatment layer  252 C by growing. Next, a third well layer  253 B is deposited on the third barrier layer  253 A by growing. Next, flow TMIn and NH 3  into the chamber to grow a third InN treatment layer  253 C on the third well layer  253 B. 
   Thereafter, a fourth barrier layer  254 A is deposited on the third InN treatment layer  253 C by growing. Next, a fourth well layer  254 B is deposited on the fourth barrier layer  254 A by growing. Next, flow TMIn and NH 3  into the chamber to grow a fourth InN treatment layer  254 C on the fourth well layer  254 B. 
   Thereafter, a fifth barrier layer  255 A is deposited on the fourth InN treatment layer  253 C by growing. Next, a fifth well layer  255 B is deposited on the fifth barrier layer  255 A by growing. Next, flow TMIn and NH 3  into the chamber to grow a fifth InN treatment layer  255 C on the fifth well layer  255 B. 
   Finally, a sixth barrier layer  256 A is deposited on the fifth InN treatment layer  255 C by growing. An LED has an MQW structure is formed. 
   Referring to  FIG. 4 , it is an atomic force microscopy (AFM) photograph showing Y direction (μm) versus X direction (μm) for samples (a), (b), (c) and (d) utilized in the invention. The sample (a) shows a single quantum well layer without TMIn treatment. The sample (b) shows a single quantum well layer with TMIn treatment. The sample (c) shows an MQW layer without TMIn treatment. The sample (d) shows an MQW layer with TMIn treatment. 
   A result of these sample treatments are listed in the following table. 
   
     
       
             
             
           
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
                 
             
             
                 
               Sample 
             
           
        
         
             
                 
               (a) 
               (b) 
               (c) 
               (d) 
             
             
                 
                 
             
           
        
         
             
               RMS Roughness (nm) 
               0.67 
               0.58 
               1.67 
               0.82 
             
             
               Density of V-defects 
               3.9 × 10 8   
               2.9 × 10 8   
               7.8 × 10 8   
               4.7 × 10 8   
             
             
               (cm −2 ) 
             
             
                 
             
           
        
       
     
   
   It is found that root mean square (RMS) roughness of a single quantum well layer or MQW layer (e.g., the InGaN/GaN MQW active layer  250 ) is decreased significantly after treating with TMIn according to the invention. 
   Referring to  FIG. 5 , it plots integrated PL (photoluminance) intensity (a.u.) versus temperature (1000/T (K −1 )) for the sample (c) having an MQW without TMIn treatment and the sample (d) having an MQW with TMIn treatment. It is found that activation energy (Ea) of an MQW layer (e.g., the InGaN/GaN MQW active layer  250 ) is increased from 49 meV to 57 meV after treating with TMIn according to the invention. Also, light emission strength decrease is maintained to a minimum. 
   Referring to  FIG. 6 , it plots output power versus current for the sample (e) showing an LED structure without TMIn treatment and the sample (f) showing an LED structure with TMIn treatment. It is found that light emission strength of the LED structure  200  is increased greatly after treating with TMIn according to the invention. 
   Referring to  FIG. 7 , it is a transmission electron microscopy (TEM) photograph showing a quantum well (a) with TMIn treatment and a quantum well (b) without TMIn treatment. It is found that surface of the quantum well is more flat after treating with TMIn according to the invention. 
   Referring to  FIG. 8 , it is a sectional view showing the constituent layers of InN quantum dots LED structure  300  manufactured according to the method of the invention. From bottom to top, there are grown of the following components. A sapphire substrate  310  is on the bottom. A GaN un-doped buffer layer  315  is deposited on the sapphire substrate  310  by growing. A GaN doped silicon N-type contact layer  320  is deposited on the GaN un-doped buffer layer  315  by growing. A GaN un-doped N-type layer  330  is deposited on the GaN doped silicon N-type contact layer  320  by growing. An InGaN un-doped strain layer  340  is deposited on the GaN un-doped N-type layer  330  by growing. An InN surface treatment layer  350  is deposited on the InGaN un-doped strain layer  340  by flowing TMIn and NH 3  into the chamber. An InN quantum dots (QDs) active layer  360  is deposited on the InN surface treatment layer  350  by growing. An InGaN un-doped strain layer  370  is deposited on the InN QDs active layer  360  by growing. An AlGaN magnesium electron blocking layer  380  is deposited on the InGaN un-doped strain layer  370  by growing. Finally, a GaN doped magnesium P-type contact layer  390  is deposited on the AlGaN magnesium electron blocking layer  380  by growing. 
   Referring to  FIG. 9 , it is a sectional view showing the constituent layers of a HBT structure  400  manufactured according to the method of the invention. From bottom to top, there are grown of the following components. A sapphire substrate  410  is on the bottom. A GaN un-doped buffer layer  420  is deposited on the sapphire substrate  410  by growing. A GaN doped silicon sub-emitter layer  430  is deposited on the GaN un-doped buffer layer  420  by growing. A GaN un-doped emitter layer  440  is deposited on the GaN doped silicon sub-emitter layer  430  by growing. A GaN doped magnesium base layer  450  is deposited on the GaN un-doped emitter layer  440  by growing. An InN surface treatment layer  460  is deposited on the GaN doped magnesium base layer  450  by growing. An InGaN doped magnesium base layer  470  is deposited on the InN surface treatment layer  460  by flowing TMIn and NH 3  into the chamber. Finally, a GaN collector layer  480  is deposited on the InGaN doped magnesium base layer  470  by growing. Surface of the HBT structure  400  has a relatively low roughness. 
   Referring to  FIG. 10 , it is a sectional view showing the constituent layers of a HEMT structure  500  manufactured according to the method of the invention. From bottom to top, there are grown of the following components. A sapphire substrate  510  is on the bottom. A GaN un-doped buffer layer  520  is deposited on the sapphire substrate  510  by growing. A GaN un-doped channel layer  530  is deposited on the GaN un-doped buffer layer  520  by growing. An InN surface treatment layer  540  is deposited on the GaN un-doped channel layer  530  by flowing TMIn and NH 3  into the chamber. An AlN un-doped layer  550  is deposited on the InN surface treatment layer  540  by growing. Finally, an AlGaN un-doped layer  560  is deposited on the AlN un-doped layer  550  by growing. Surface of the HEMT structure  500  has a relatively low roughness. 
   Referring to  FIG. 11 , it is a sectional view showing the constituent layers of a rectifier structure  600  manufactured according to the method of the invention. From bottom to top, there are grown of the following components. A sapphire substrate  610  is on the bottom. A GaN un-doped buffer layer  620  is deposited on the sapphire substrate  610  by growing. A GaN un-doped channel layer  630  is deposited on the GaN un-doped buffer layer  620  by growing. An InN surface treatment layer  640  is deposited on the GaN un-doped channel layer  630  by flowing TMIn and NH 3  into the chamber. An AlN un-doped layer  650  is deposited on the InN surface treatment layer  640  by growing. An AlGaN un-doped layer  660  is deposited on the InN un-doped layer  650  by growing. A GaN un-doped layer  670  is deposited on the AlGaN un-doped layer  660  by growing. Finally, a GaN doped magnesium P-type layer  680  is deposited on the GaN un-doped layer  670  by growing. Surface of the rectifier structure  600  has a relatively low roughness. 
   The nitride semiconductor material grown by the method of the invention can be applied to the manufacturing of LED. 
   While the invention herein disclosed has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.