臺灣博碩士論文加值系統

在本論文中，我們利用有機金屬氣相磊晶法(MOVPE)成長及研究氮化物半導體材料特性，包含未摻雜、n-型及p-型氮化鎵(GaN)與矽摻雜氮化銦鎵(InGaN)及氮化鎵/氮化銦鎵(GaN/InGaN)多層量子井(MQW)結構。另外也成功利用有機金屬氣相磊晶法(MOVPE)來成長氮化鎵/氮化銦鎵(GaN/InGaN)多層量子井(MQW)結構黃色、綠色、藍色及紫外發光二極體(LED)。在單一材料的磊晶品質上，氮化鎵薄膜在1150℃的高溫下成長，其X光束繞射頻譜(XRD)在(002)及(102)面均可得到較小的半高寬(FWHM)，其背景濃度與霍爾遷移率(mobility)分別可達到3.26×1016 cm-3及543 cm2/Vs。此外，對於n-型與p-型氮化鎵薄膜，我們可以精確的控制其摻雜濃度，另外也藉由低溫光激發量測(PL)與霍爾量測來測量其發光頻譜及得知其材料特性與摻雜機制。
元件級之氮化銦鎵薄膜及其相關之多層量子井(MQW)結構是發展製作高亮度發光二極體之技術重點。在我們的研究中發現，氮化銦鎵薄膜及其相關之多層量子井(MQW)結構中之銦(Indium)含量及磊晶品質明顯受到成長溫度與氣體流量之影響，其相關發光波長也會隨之改變。在LED的製程方面，我們使用Cl2/Ar作為反應氣體來研究乾蝕刻技術，可獲得高蝕刻速率，並且加入CH4和N2來製造鏡面似的橫切面，其蝕刻底部也相當平坦。對於n-型接觸電極方面，使用Ti/Al作為接觸電極，並研究回火溫度及回火時間對於特徵電阻值的影響；對於p-型接觸電極方面，使用Ni/Au作為接觸電極，研究其厚度對於特徵電阻值的影響。
根據先前磊晶與製程經驗，我們可以製作出綠色發光二極體，並且應用電荷非對稱型共振穿透結構(CART)和布拉格反射器(DBR)來製作高亮度發光二極體。在20mA的驅動電流下其順向偏壓可由3.7V降至3.2V，而且其功率及發光效率可達7.2mW和11.25%，同時良率可達80%以上。此外，在藍色及紫外發光二極體方面，在20mA的驅動電流下其發光波長及功率分別為466nm及8mW與400nm及1.5mW。最後我們嘗試以簡單結構製作黃色發光二極體，其發光波長為570nm。
利用銦錫氧化物(ITO)、Au、Ni及Pt作為電極來製作金屬-半導體-金屬型紫外光檢測器(MSM UV detector)，經過600℃熱處理，ITO可達到98%的高穿透率。利用這種ITO透明電極作成的檢測器具有高響應特性為7.2A/W，且這樣的高響應特性會因此降低其3-dB頻率特性,其反應速度也隨之變慢。另外，我們也針對氮化鎵與氮化鋁鎵(GaN/AlGaN)介面之二維電子雲(2DEG)作探討，並利用這種結構與圓環型光罩設計來製作平面型場效電晶體(Round FET)，在Vg = -1.5V時，其最大轉導值(Gm)可達101 mS/mm。

In this dissertation, the growth and characteristics of the III-V nitrides semiconductor that consist of undoped GaN, n-type GaN, p-type GaN, Si-doped InGaN layers, and InGaN/GaN MQW had been systematically studied. Using MOCVD techniques, the InGaN/GaN MQW green, blue, and yellow LEDs were successfully fabricated. In epitaxial layers growth, we discovered the growth temperature of GaN epitaxial layers strongly influence the optical and electric properties. In addition, it can be seen that the high temperature GaN epitaxial layers grown under 1150℃ had a small FWHM of (002) and that of (102). The background carrier concentration and mobility were as low as 3.26×1016 cm-3 and 543 cm2/Vs, respectively. For Si-doped GaN, controllable doping of n-type GaN grown by MOCVD has been achieved over a wide range of 5×1016cm-3 to 1×1019cm-3. For Mg-doped GaN, this work investigated the basic theory of p-type GaN, which is activated in nitrogen ambient. Then, the low temperature PL and hall measurement have discussed at the same time.
For LED chips process, it is necessary to use the dry etching technique. In the present work by using reactive ion etching we have obtained the highest etch rate of about 505 Å/min and 448 Å/min for n- and p-GaN, respectively. When CH4 is added to the BCl3/Ar plasma, the etch rate is decreased. The addition of N2 does not influence the etching rate significantly. However, due to slower etching rates, the resultant etched surface becomes smoother. The etched sidewall in the present study makes an angle of 15o with the etched plane. Using these etching parameters, mirrorlike facets can be obtained which can be used for the fabrication of nitride-based LDs and LEDs. Therefore, the standard InGaN/GaN MQW LED can be fabricated from epitaxy to device process. For LED, we have applied CART and DBR structures to nitride-based green LED and experimentally show that CART and DBR structures can both enhance the performance of the nitride-based green LED. It was found that we could reduce the forward voltage at 20mA from 3.7V to 3.2V with the inclusion of CART structure. It was also found that the EL peak wavelength of the CART LED is less sensitive to the amount of injection current. The output power and external quantum efficiency of the CART LED with DBR structure measured at 20 mA can reach 7.2 mW and 11.25%, respectively. Furthermore, the 505nm and 525nm green LEDs were successfully under mass production by more than 80% yield of LED chips. On the other hand, the InGaN/GaN MQW blue and UV LEDs were also discussed in this chapter. The output power and peak wavelength were 8mW, 466nm, and 1.5mW, 400nm, respectively. We also discussed about the nitride-based yellow LED and show their PL, EL, and CIE characteristics. It might be not a good method to produce yellow LED by using so lots of indium mole fraction in the MQW.
ITO, Au, Ni and Pt layers were deposited onto n-GaN films and/or glass substrates by electron-beam evaporation. With proper annealing, it was found that we could improve the optical properties of the ITO layers and achieve a maximum transmittance of 98% at 360nm. GaN-based MSM UV sensors with ITO, Au, Ni and Pt as contact electrodes were also fabricated. It was found that we could achieve a maximum 0.12A photocurrent and a photocurrent to dark current contrast higher than five orders of magnitude for the 600oC-annealed ITO/n-GaN MSM UV sensor under 5V bias voltage. We also found that the maximum responsivity at 345nm was 7.2 A/W and 0.9 A/W when the 600oC-annealed ITO/n-GaN MSM UV sensor was biased at 5V and 0.5V, respectively. These values were much larger than those observed from other metal/n-GaN MSM UV sensors. However, the existence of photoconductive gain in the 600oC-annealed ITO/n-GaN MSM UV sensor also results in a slower operation speed and a smaller 3-dB bandwidth as compared with the metal/n-GaN MSM UV sensors. Besides, the 2DEG behavior between the AlGaN/GaN heterojunction was discussed completely. The “Round FET” process was proposed to use for HEMT fast process. By this skill we had succeed demonstrated the DC characteristics of the AlGaN/GaN HEMT. The maximum transconductance Gm = 101 mS/mm was measured at the gate bias Vg = -1.5V. The reverse gate current was still lower than 5×10-5 A when the gate to source reverse bias voltage is –10V. The turn on voltage of the Schottky contact is around 1.5V.

Contents
CHAPTER 1 Introduction
1-1 The History of Research on III-Nitrides …………………………………… 1
1-2 The MOVPE Growth Methods of III-Nitrides …………………………… . 5
1-3 Overview of This Dissertation …………………………………………….. 7
References ……………………………………………………………………… 9
CHAPTER 2 Crystal Growth and Characterization of Gallium Nitride Epilayers
2.1 Growth Theory ……………………………………………………………. 16
2.2 The Growth of Nucleation Layer and Undoped GaN …………………….. 20
2.3 Si-doped GaN Growth ……………………………………………………. 23
2.4 Mg-doped GaN Growth …………………………………………………... 27
References …………………………………………………………………….. 33
CHAPTER 3 Crystal Growth of InGaN Layers and InGaN/GaN MQW
3.1 Growth of InxGa1-xN Epilayers……………………………………………. 52
3.2 Growth of InxGa1-xN/GaN Multiple Quantum Well …………………….….59
References …………………………………………………………………….. 63
CHAPTER 4 GaN Based Device Processes
4.1 Dry Etching of GaN Using RIE ….………………………………………...77
4.2 Study of Ti/Al Ohmic Contacts for N-GaN…………………………………81
4.3 Study of Ni/Au Ohmic Contacts for P-GaN……..………………………….84
References………………………………………………………………………87
Chapter 5 InGaN/GaN MQW Light Emitting Diodes
5.1 The Brightness Green Light Emitting Diodes……………………………..106
5.2 InGaN/GaN MQW blue and UV LED…………………………………….118
5.3 InGaN/GaN MQW Yellowish green LED ………………………………...121
References……………………………………………………………………..125
Chapter 6 The Study of Other Optoelectronic Devices
6.1 The GaN metal-semiconductor-metal ultraviolet sensors ………………...153
6.2 The GaN Based FET …………………………………………………..….162
References………………………………………………………………………..166
Chapter 7 Conclusion ………………………………………………………...191

Reference
[1] R. juza and H. Hahn, Anorg. Allegem. Chem., Vol.234, p.282, 1940.
[2] H. P. Maruska and J. J. Tietjen, Appl. Phys. Lett., Vol.15, p.367, 1969.
[3] J. I. Pnakove, E. A. Miller, D. Richman and J. E. Berketheiser, J. Lumin., Vol.4, p.63, 1971.
[4] H. P. Maruska, W. C. Rhines and D. A. Stevendson, “Preparation of Mg-Doped GaN Diodes Exhibiting Violet Electroluminescence,” Mater. Res. Bull., Vol.7, pp.777-782, 1972.
[5] H. Amano, N. Sawaki, I. Akasaki and Y. Toyoda, “Metalorganic vapor phase epitaxial growth of a high quality GaN film using an AlN buffer layer,” Appl. Phys. Lett., Vol.48, pp.353-355, 1986.
[6] H. Amano, M. Kito, K. Hiramatsu and I. Akasaki, “P-type Conduction in Mg-Doped GaN Treated with Low-Energy Electron Beam Irradiation (LEEBI),” Jpn. J. Appl. Phys., Vol.28, pp.L2112-L2114, 1998.
[7] S. Nakamura, T. Mukai, M. Senoh and N. Iwasa, “Thermal Annealing Effects on P-Type Mg-Doped GaN Films,” Jpn. J. Appl. Phys., Vol.31, pp.L139-L142, 1992.
[8] See the series books of “SEMICONDUCTORS AND SEMIMETALS,” Vol.50, “Gallium Nitride” edited by J. I. Pankove., page 22, Figure 6.
[9] Bernard Gil, “ Group III nitride Semiconductor Compounds”, p.33 (Clarendon Press, Oxford, 1998).
[10] S. D. Lester, F. A. Ponce, M. G. Graford, and D. A. Steigerwald, “High dislocation densities in high efficiency GaN-based light-emitting diodes,” Appl. Phys. Lett., Vol.66, pp.1249-1251, 1995.
[11] S. Nakamura, M. Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, H. Kiyoku, Y. Sugimoto, T. Kozaki, H. Umemoto, M. Sano, and K. Chocho, “InGaN/GaN/AlGaN-based laser diodes with modulation-doped strained-layer superlattices grown on an epitaxially laterally overgrown GaN substrate,” Appl. Phys. Lett., Vol.72, pp.211-213, 1998.
[12] H. Amano, M. Kito, K. Hiramatsu and I. Akasaki, “P-type Conduction in Mg-Doped GaN Treated with Low-Energy Electron Beam Irradiation (LEEBI),” Jpn. J. Appl. Phys., Vol.28, pp.L2112-L2114, 1998.
[13] S. Nakamura, T. Mukai, M. Senoh and N. Iwasa, “Thermal Annealing Effects on P-Type Mg-Doped GaN Films,” Jpn. J. Appl. Phys., Vol.31, pp.L139-L142, 1992.
[14] S. Nakamura, N. Iwasa, Senoh, and T. Mukai, “Hole Compensation Mechanism of P-type GaN Films,” Jpn. J. Appl. Phys., Vol.31, pp.1258-1266, 1992.
[15] E. L. Piner, M. K. Behbehani, N. A. Ei-Masry, F. G. McIntosh, J. C. Roberts, K. S. Boutros and S. M. Bedair, “Effect of hydrogen on the indium incorporation in InGaN epitaxial films,“ Appl. Phys. Lett., Vol.70, pp.461-463, 1997.
[16] M. Kazumura, I. Ohta, and I. Teramoto, “Feasibility of the LPE growth of AlxGayIn1-xP on GaAs substrate,” Jpn. J. Appl. Phys., Vol.22, pp.654, 1983.
[17] S. Nakamura, Jpn. J. Appl. Phys., “GaN Growth Using GaN Buffer Layer,” Vol.30, pp.L1705-L1707, 1991.
[18] S. Nakamura, T. Mokia and M. Senoh, “Candela-class high-brightness InGaN/AlGaN double-heterostructure blue-light-emitting diodes,” Appl. Phys. Lett., Vol.64, pp.1687-1689, 1994.
[19] C. P. Kuo, R. M. Fletcher, T.D. Osentowski, M. C. Lardizabal, M. G. Craford, and V. M. Robbins, “High performance AlGaInP visible light-emitting diodes,” Appl. Phys. Lett., Vol.57, pp.2937-2939, 1990.