本文選題：選擇性橫向外延生長(zhǎng) + 半極性面GaN材料與器件�。� 參考：《南京大學(xué)》2016年博士論文

【摘要】：Ⅲ族氮化物材料帶隙從0.7 eV到6.2 eV連續(xù)變化,波長(zhǎng)覆蓋了從近紅外到紫外極為寬廣的光譜范圍,具有優(yōu)異的光電特性,具有比其他材料更大的應(yīng)用范圍和更高的發(fā)光效率。這些優(yōu)點(diǎn)使氮化物L(fēng)ED成為目前最成功的近紫外到藍(lán)綠光的發(fā)光器件。然而氮化物異質(zhì)結(jié)構(gòu)是強(qiáng)極化、高應(yīng)變的量子體系,極化不連續(xù)性引入極強(qiáng)內(nèi)建電場(chǎng),導(dǎo)致量子阱結(jié)構(gòu)中電子空穴波函數(shù)的空間分離,降低了發(fā)光效率。趨向于無(wú)極化的研究思路,非極性面和半極性面的GaN基LED的研究逐漸得到重視,其中極化效應(yīng)的減弱會(huì)帶來(lái)更加優(yōu)異的光電特性和巨大的潛在應(yīng)用。非極性面和半極性面GaN的材料外延缺少合適的襯底,自支撐襯底成本高尺寸小,異質(zhì)襯底外延的晶體質(zhì)量較差,難以達(dá)到較高的發(fā)光效率。于是,利用選擇性橫向外延技術(shù)在c面藍(lán)寶石襯底上生長(zhǎng)半極性面GaN材料和發(fā)光器件,可以有效降低位錯(cuò)密度,易于制備不同半極性面的材料和器件。本論文圍繞半極性面GaN材料及器件光電性質(zhì)展開(kāi)研究,探索了半極性面GaN選擇性橫向外延的生長(zhǎng)規(guī)律,研究了半極性面GaN的位錯(cuò)變化機(jī)制和光學(xué)性質(zhì)；系統(tǒng)研究了半極性面InGaN/GaN多量子阱的光學(xué)性質(zhì),比較了半極性面和極性面InGaN/GaN多量子阱的極化特性,證明了半極性面InGaN/GaN多量子阱優(yōu)異的發(fā)光特性；制備出半極性面InGaN/GaN多量子阱LED器件,探討了器件制備過(guò)程的關(guān)鍵技術(shù)問(wèn)題,研究了半極性面LED器件的光學(xué)性質(zhì)和電學(xué)性質(zhì)。研究的主要內(nèi)容和獲得的主要結(jié)果如下：1.分析了不同取向不同尺寸不同維度的掩膜圖形上選擇性橫向外延生長(zhǎng)半極性面的成面機(jī)制,證明不同晶面的形成取決于晶面表面能和表面原子的穩(wěn)定性。研究發(fā)現(xiàn)在沿[11-20]和[1-100]方向的條形掩膜上進(jìn)行選擇橫向外延生長(zhǎng),會(huì)分別形成{1-101)和{11-22}半極性面,{1-101}面的穩(wěn)定性優(yōu)于{11-22}面。在十字掩膜上選擇橫向外延生長(zhǎng)會(huì)形成三種半極性面{1-101}、{21-33)和{11-22},其中{21-33}面會(huì)隨著生長(zhǎng)溫度升高而由于熱穩(wěn)定性差而消失。系統(tǒng)研究了生長(zhǎng)溫度和掩膜填充因子等參數(shù)對(duì)半極性面微面結(jié)構(gòu)形貌和不同晶面生長(zhǎng)速度的影響。研究發(fā)現(xiàn)溫度升高和掩膜填充因子增加都能夠增加反應(yīng)原子的表面遷移能力,有利于橫向外延生長(zhǎng)形成表面能較低的(0001)晶面。研究表明反應(yīng)過(guò)程的生長(zhǎng)速度是由質(zhì)量輸運(yùn)控制。2.研究發(fā)現(xiàn)選擇性橫向外延半極性面GaN生長(zhǎng)技術(shù)能有效減小位錯(cuò)密度,掩膜填充因子增大和掩膜維度增加能更有效的減小位錯(cuò)密度,提高晶體質(zhì)量。系統(tǒng)分析了半極性面GaN材料的光學(xué)性質(zhì),低溫PL譜觀測(cè)到了分別來(lái)源于基面堆垛層錯(cuò)(BSF)和棱柱堆垛層錯(cuò)(PSF)的3.41 eV和3.29 eV附近的發(fā)光峰,證實(shí)了半極性面GaN中基面堆垛層錯(cuò)(BSF)主要是在橫向外延區(qū)域產(chǎn)生。變溫PL譜發(fā)現(xiàn)半極性面GaN材料近帶邊發(fā)射峰(NBE)的發(fā)光峰位隨著溫度的升高而紅移,服從通常的能帶收縮效應(yīng)。而基面堆垛層錯(cuò)(BSF)發(fā)光峰位則隨溫度呈現(xiàn)S形非單調(diào)變化,原因是由于基面堆垛層錯(cuò)引起的導(dǎo)帶和價(jià)帶不連續(xù)性會(huì)導(dǎo)致載流子的局域化。3.對(duì)于選擇性橫向外延生長(zhǎng)的半極性面InGaN/GaN多量子阱,相同生長(zhǎng)條件下半極性面{11-22}、{1-101}和極性面(0001)的發(fā)光峰位分別為412 nm、436nm518 nm,并且同一個(gè){1-101}晶面中頂部發(fā)光峰位相比底部發(fā)生了23nm的紅移。發(fā)光峰位發(fā)生差異的主要原因是不同晶面甚至同一半極性面不同位置的生長(zhǎng)速度不同,導(dǎo)致了多量子阱阱寬和In摻雜效率不同,另外選擇性橫向外延生長(zhǎng)過(guò)程中的In原子遷移長(zhǎng)度大于Ga,也會(huì)導(dǎo)致In的組分發(fā)生差異從而影響發(fā)光峰位。研究表明十字掩膜上生長(zhǎng)形成的三種半極性面InGaN/GaN多量子阱的發(fā)光波長(zhǎng)順序?yàn)閧1-101}{21-33}{11-22},與這些晶面的生長(zhǎng)速度順序一致。發(fā)現(xiàn)微面結(jié)構(gòu)中c面頂面量子阱的團(tuán)簇分布的不均勻發(fā)光現(xiàn)象,證明了相比半極性面斜面,c面頂面有著較高的位錯(cuò)密度而導(dǎo)致其InGaN生長(zhǎng)過(guò)程中出現(xiàn)相分凝。4. 變功率PL研究發(fā)現(xiàn)半極性面多量子阱的發(fā)光峰位隨激光功率增加的藍(lán)移量?jī)H為極性c面的1/5,證明了半極性面多量子阱極化電場(chǎng)大幅減小,QCSE效應(yīng)大幅減弱。計(jì)算得到{1-101}和{11-22}半極性面InGaN/GaN多量子阱的內(nèi)量子效率ηint分別為65.6%和55.7%,遠(yuǎn)高于c面多量子阱的內(nèi)量子效率(15.9%),證實(shí)了限制極化電場(chǎng)導(dǎo)致的QCSE效應(yīng)能夠大幅提高InGaN/GaN多量子阱的發(fā)光性能。變溫PL研究表明半極性面InGaN/GaN多量子阱的PL發(fā)光峰能量隨溫度升高而單調(diào)下降,不同于極性c面多量子阱中由于載流子局域化導(dǎo)致的“S”型關(guān)系曲線,是由于半極性面多量子阱中的弱極化電場(chǎng)和深阱使得載流子局域化效應(yīng)減弱導(dǎo)致。建立了應(yīng)變誘導(dǎo)極化模型,經(jīng)過(guò)計(jì)算證明了半極性面InGaN/GaN多量子阱的壓電極化強(qiáng)度和總極化強(qiáng)度比極性c面大幅減小,使得能帶變平,發(fā)光峰藍(lán)移,QCSE效應(yīng)減弱,輻射復(fù)合效率提高。5.研制出了半極性面InGaN/GaN多量子阱LED器件,發(fā)現(xiàn)Mg摻雜能夠增強(qiáng)Ga原子的遷移能力,促進(jìn)橫向生長(zhǎng)使得半極性面pGaN層厚度遠(yuǎn)大于極性c面。研究了半極性面LED的光學(xué)性質(zhì),證明了{(lán)11-22}半極性面相比極性c面,極化電場(chǎng)大幅減小,QCSE效應(yīng)大幅減弱。Ⅰ-Ⅴ特性結(jié)果發(fā)現(xiàn)制得的半極性面LED芯片的正向電壓為6.3 V,反向漏電流為2 mA@-5 V,均弱于極性c面LED芯片的電性,主要是由于選擇性橫向外延中pGaN的外延生長(zhǎng)工藝和非平面芯片的金屬蒸鍍工藝造成,表明半極性面LED的外延及芯片工藝還有待進(jìn)一步優(yōu)化。
[Abstract]:The band gap of III nitride materials varies from 0.7 eV to 6.2 eV, and the wavelength covers a wide spectrum range from near infrared to ultraviolet. It has excellent photoelectric properties, and has larger application range and higher luminous efficiency than other materials. These advantages make the nitride LED the most successful near ultraviolet to blue and green light. However, the nitride heterostructure is a strong polarization, high strain quantum system, and polarization discontinuity is introduced into the extremely strong internal electric field, which leads to the space separation of the electron hole wave function in the quantum well structure and the reduction of the luminescence efficiency. The research trend of the polarization is not polarized, and the research of the GaN based LED of the non polar and semi polar surfaces has been gradually paid attention to, The weakening of the polarization effect will bring more excellent photoelectric properties and huge potential applications. The material epitaxy of non polar and semi polar surface GaN is lack of suitable substrate, the cost of self supported substrate is high, the crystal quality of the heteroepitaxial substrate is poor, and it is difficult to achieve high luminous efficiency. The growth of semi polar surface GaN materials and light emitting devices on C surface sapphire substrate can effectively reduce dislocation density and be easy to prepare materials and devices with different semi polar surfaces. This paper studies the photoelectric properties of GaN materials and devices on semi polar surfaces, and explores the growth law of the semi polar surface GaN selective lateral epitaxy. The dislocation mechanism and optical properties of polar surface GaN, the optical properties of the semi polar InGaN/GaN multiple quantum well are studied systematically, and the polarization characteristics of the semi polar and polar InGaN/GaN multiple quantum well are compared. The excellent luminescence characteristics of the semi polar InGaN/GaN multiple quantum well are proved and the semi polar InGaN/GaN multi quantum well LED device is prepared. The key technical problems of the device preparation process are discussed and the optical and electrical properties of the semi polar surface LED devices are studied. The main contents and main results are as follows: 1. the surface mechanism of the selective lateral extension of the semi polar surface on the mask patterns with different dimensions and different dimensions is analyzed. The formation of the isomorphic surface depends on the surface energy and the stability of the surface atoms. It is found that the selective lateral epitaxial growth on the strip mask along the [11-20] and [1-100] directions will form {1-101) and the {11-22} semi polar surface respectively. The stability of the {1-101} surface is better than that of the {11-22} surface. The selection of lateral epitaxial growth on the cross mask will form three. A semi polar surface {1-101}, {21-33) and {11-22}, in which the {21-33} surface will disappear with the increase of the growth temperature and due to the poor thermal stability. The influence of the growth temperature and the mask filling factor on the microstructure and the growth speed of the semi polar surface micro surface and the growth rate of the different crystal surfaces is investigated. It is possible to increase the surface mobility of the reaction atoms, which is beneficial to the formation of a surface with lower surface energy (0001). The study shows that the growth rate of the reaction process is based on the mass transport control.2.. It is found that the selective lateral epitaxial semi polar surface GaN growth technique can reduce the dislocation density effectively, the mask filling factor increases and the mask can be masked. The dimension increase can reduce the dislocation density more effectively and improve the crystal quality. The optical properties of the semi polar GaN materials are systematically analyzed. The low temperature PL spectra have observed the luminescence peaks near the 3.41 eV and 3.29 eV, which are derived from the stacking fault (BSF) and the prism stacking fault (PSF) respectively, and confirmed the main surface stacking fault (BSF) in the semi polar GaN. It is produced in the lateral epitaxial region. The variation of temperature PL spectra shows that the luminescence peak of the near band edge emission peak (NBE) of the semi polar surface GaN material is redshift with the increase of temperature, and it obeys the usual band contraction effect. The luminescence peak of the base stacking stacking fault (BSF) is not monotonically changed with the temperature of S, due to the conduction band caused by the stacking fault of the base surface. The valence band discontinuities lead to the localization of the carrier.3. for the semi polar InGaN/GaN multiple quantum well with selective lateral epitaxy. The luminescence peaks of the semi polar surface {11-22}, {1-101} and polar surface (0001) under the same growth conditions are 412 nm and 436nm518 nm respectively, and the bottom of the top luminescence peak in the same {1-101} crystal surface occurs at the bottom. The main reason for the difference of the luminescence peak is that the growth rate of the different crystal surface and even the same half polar face is different, which leads to the different quantum well well width and the In doping efficiency. In addition, the In atom migration length in the selective lateral epitaxial growth is greater than that of the Ga, and the difference in the component of the In will result in the shadow of the In. The study shows that the luminescence wavelength of the three semi polar InGaN/GaN quantum well formed on the cross mask is {1-101}{21-33}{11-22}, which is in the same order as the growth rate of these crystal surfaces. It is found that the uneven luminescence of the cluster distribution of the top surface of the C surface in the surface of the micro surface proves that the half polar surface is compared with the semi polar surface. There is a high dislocation density on the top surface of the C surface, which leads to the phase segregation of.4. in the process of InGaN growth. It is found that the blue shift of the luminescence peak of the semi polar multi quantum well with the increase of laser power is only 1/5 of the polar C surface. It is proved that the polarization electric field of the semi polar multi quantum well is greatly reduced and the QCSE effect is greatly weakened. The internal quantum efficiency of the {1-101} and {11-22} semi polar InGaN/GaN quantum wells is 65.6% and 55.7% respectively, which is far higher than the internal quantum efficiency (15.9%) of the C multi quantum well. It is proved that the QCSE effect caused by the restricted polarization field can greatly improve the luminescence energy of the InGaN/GaN multi quantum well. The variable temperature PL study shows that the semi polar face is InGaN/GaN multiple. The PL luminescence peak energy of the sub well decreases monotonously with the increase of temperature. It is different from the "S" relationship curve caused by the carrier localization in the polar C multi quantum well. It is due to the weak polarization electric field and deep well in the semi polar multi quantum well which weakens the carrier localization effect. The strain induced polarization model is established. It is proved that the piezoelectric polarization intensity and the total polarization intensity of the semi polar InGaN/GaN multi quantum well are greatly reduced than the polar C surface, making the energy band leveling, the blue shift of the luminescence peak, the QCSE effect weakened, the radiation recombination efficiency improved by.5., and the semi polar InGaN/GaN multi quantum well LED device is developed. The occurrence of Mg doping can enhance the migration ability of Ga atoms and promote the migration of Ga atoms. The thickness of the semi polar surface pGaN layer is far larger than the polar C surface. The optical properties of the semi polar surface LED are studied. It is proved that the {11-22} semi polar face is compared to the polar C surface, the polarization electric field is greatly reduced and the QCSE effect is greatly weakened. The positive voltage of the semi polar plane LED core is 6.3 V and the reverse leakage current is 2 mA@-. The electrical properties of 5 V, which are all weaker than the polar C LED chips, are mainly due to the epitaxial growth process of pGaN in selective lateral epitaxy and the metal evaporation process of non planar chips, indicating that the epitaxy of the semi polar LED and the chip technology still need to be further optimized.
【學(xué)位授予單位】：南京大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TN304.2

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