本文選題：發(fā)光二極管 + GaN�。� 參考：《太原理工大學(xué)》2016年博士論文

【摘要】：LED作為第三代光源,具有節(jié)能、環(huán)保、壽命長、穩(wěn)定性高、體積小等優(yōu)點(diǎn),可以廣泛應(yīng)用于各種指示、顯示、裝飾、背光源和固態(tài)照明等領(lǐng)域。自中村修二成功制備了寬禁帶GaN基半導(dǎo)體材料之后,具有商業(yè)應(yīng)用價(jià)值的藍(lán)光LED獲得實(shí)現(xiàn),LED在光效提升和成本降低方面取得了飛速的發(fā)展。但LED仍有一些問題需要進(jìn)一步解決和完善,例如,外延生長參數(shù)對GaN晶體質(zhì)量的影響機(jī)制還不明確;高空穴濃度低電阻率p型GaN的制備困難;InGaN與GaN的物理化學(xué)性能差異使得高質(zhì)量量子阱生長困難等。本論文從以上提出的問題出發(fā),對GaN基LED外延結(jié)構(gòu)各功能層進(jìn)行生長,探究了工藝參數(shù)和結(jié)構(gòu)參數(shù)對不同功能層結(jié)構(gòu)性質(zhì)以及光電性能的影響,并對其影響機(jī)制做了深入的分析。具體內(nèi)容如下:1、研究了形核層厚度(分別為15、25和45 nm)對平面藍(lán)寶石襯底上生長的GaN薄膜晶體質(zhì)量的影響。高分辨X射線衍射(HRXRD)結(jié)果表明:當(dāng)形核層厚度為25 nm時(shí),GaN外延薄膜的(002)和(102)面的HRXRD譜的半高寬(FWHM)最小,分別為267和284 arcsec。原子力顯微鏡(AFM)結(jié)果表明:形核層退火后,樣品表面呈島狀結(jié)構(gòu)。形核層厚度的增加有利于獲得大尺寸的島,但是島的均勻性較差。尺寸大、均勻性好、密度低的形核島對GaN外延薄膜的晶體質(zhì)量是最有利的,這可采用位錯(cuò)的產(chǎn)生和演變機(jī)制來解釋影響機(jī)理。調(diào)控形核層厚度是控制島的尺寸和密度的有效手段之一,因此,形核層厚度能夠顯著影響gan薄膜的晶體質(zhì)量。2、研究了形核層厚度對圖形藍(lán)寶石襯底上生長的gan薄膜晶體質(zhì)量的影響。掃描電子顯微鏡(sem)和hrxrd結(jié)果表明:三維生長過程中形核點(diǎn)的位置對gan薄膜的晶體質(zhì)量有明顯的影響,當(dāng)三維生長形核點(diǎn)的位置處于圖形的側(cè)壁時(shí)不利于gan薄膜晶體質(zhì)量的提高,這是由于側(cè)壁上長大的形核島晶體取向存在差異;三維生長形核點(diǎn)的位置處于圖形的間隙時(shí)有利于獲得高質(zhì)量的gan晶體,這時(shí)形核島的晶體取向一致,生長的gan表面較平整,晶體質(zhì)量較高。形核層的厚度能夠顯著影響形核點(diǎn)的位置,因此其對gan的晶體質(zhì)量有重要的影響。3、解釋了輕si摻雜gan中較高的載流子遷移率以及較強(qiáng)的黃帶發(fā)光峰強(qiáng)度的物理機(jī)制。結(jié)果表明:載流子遷移率隨著載流子濃度的升高呈現(xiàn)出先增加后降低的變化趨勢,這種變化源自于電離雜質(zhì)對位錯(cuò)散射的屏蔽和電離雜質(zhì)散射的增強(qiáng)。在低摻雜濃度下(載流子濃度為2.37×1017cm-3),電離雜質(zhì)對位錯(cuò)散射的屏蔽作用處于主導(dǎo)地位,從而導(dǎo)致遷移率的驟升。在高的摻雜濃度下(載流子濃度為9.73×1018cm-3),電離雜質(zhì)散射的增強(qiáng)導(dǎo)致載流子遷移率的降低。高的遷移率導(dǎo)致光生非平衡載流子的擴(kuò)散長度增加,從而引起更多的缺陷參與到復(fù)合中去,導(dǎo)致輕si摻雜gan的黃帶發(fā)光峰強(qiáng)度增強(qiáng)。4、研究了mg/ga比對p型gan光電性能的影響。結(jié)果表明:當(dāng)mg/ga比為2%時(shí),p型gan可以獲得最高的空穴濃度4.2×1017cm-3。當(dāng)mg/ga比超過了2%時(shí),會形成位于深施主能級的mgga-vn,起自補(bǔ)償作用,此時(shí),440nm的藍(lán)光發(fā)光峰會出現(xiàn),并且隨著mg/ga比的不斷增大,440nm的藍(lán)光發(fā)光峰逐漸增強(qiáng)。同時(shí),較大的Mg/Ga比會導(dǎo)致p型GaN表面出現(xiàn)顆粒狀的物質(zhì),并且隨著比值的增加,顆粒的尺寸增大。結(jié)果表明在重?fù)诫s狀態(tài)下,Mg雜質(zhì)并不是全部以受主狀態(tài)存在,而是部分以深施主狀態(tài)存在。5、研究了阱層厚度對藍(lán)光InGaN/GaN量子阱性能的影響。結(jié)果表明:在相同的激發(fā)功率下,隨著阱厚的增加,光致發(fā)光譜(PL)發(fā)光波長出現(xiàn)紅移,并且激發(fā)功率越大,紅移程度越弱。隨著阱厚的增加,對于較薄的量子阱(1.8和2.7 nm),PL發(fā)光波長的紅移是由帶隙填充效應(yīng)引起的;對于較厚的量子阱(3.6和4.5 nm),PL發(fā)光波長的紅移是由極化場屏蔽效應(yīng)引起的。阱最薄的樣品(1.8 nm)由于其極化效應(yīng)最弱,EL譜具有最高的發(fā)光強(qiáng)度,但其發(fā)光波長較短僅有430 nm,比標(biāo)準(zhǔn)的藍(lán)光波長(450 nm)藍(lán)移了20 nm。雖然,可以通過降低生長溫度或增加In源流量的方法使其發(fā)光波長變?yōu)?50 nm,但其晶體質(zhì)量會變差,導(dǎo)致EL發(fā)光強(qiáng)度比2.7 nm阱厚的樣品低,因此,在標(biāo)準(zhǔn)的藍(lán)光波段2.7 nm為較理想的阱厚。6、研究了量子阱中勢阱層的生長速率對綠光InGaN/GaN量子阱性能的影響。HRXRD結(jié)果表明:隨著勢阱層生長速率的提高,量子阱的界面質(zhì)量不斷惡化。AFM結(jié)果表明:隨著阱層生長速率的提高,量子阱表面開始出現(xiàn)裂紋,并且裂紋的尺寸逐漸增大。PL結(jié)果表明:在低的生長速率下,PL發(fā)光強(qiáng)度會明顯提高,FWHM變窄,發(fā)光波長藍(lán)移。以上結(jié)果表明降低量子阱的生長速率使勢阱中In組分分布更均勻,有利于獲得陡峭的量子阱界面和較平整的量子阱表面。
[Abstract]:LED, as the third generation light source, has the advantages of energy saving, environmental protection, long life, high stability and small volume. It can be widely used in various directions, display, decoration, backlight and solid state lighting. Since Nakamura Shuji has successfully prepared the wide band gap GaN based semiconductor materials, the blue light LED with commercial application value is realized, and LED is in light effect. The improvement and cost reduction have made rapid progress. However, there are still some problems to be solved and improved in LED. For example, the influence mechanism of the epitaxial growth parameters on the quality of GaN crystal is not clear; the preparation of P GaN with low resistivity at high altitude is difficult, and the difference of physical and chemical properties between InGaN and GaN makes the high quality quantum well growth stranded. In this paper, from the above questions, the function layer of GaN based LED epitaxial structure is grown, and the influence of process parameters and structural parameters on the structure and photoelectric properties of different functional layers is explored, and the influence mechanism is deeply analyzed. The specific contents are as follows: 1, the thickness of the nucleation layer (15,25 and 45, respectively) Nm) effect on the crystal quality of the GaN film grown on a flat sapphire substrate. The results of high resolution X ray diffraction (HRXRD) show that when the thickness of the nucleation layer is 25 nm, the HRXRD spectrum of the GaN epitaxial film is the smallest half width (FWHM) of the (002) and (102) surface, and the results of the 267 and 284 arcsec. atomic force microscopy (AFM) respectively indicate that after the nucleation layer is annealed, the sample is annealed. The increase of the thickness of the nucleation layer is beneficial to the large size of the island, but the uniformity of the island is poor. The size, uniformity, and the low density of the nucleation island are the most favorable to the crystal quality of the GaN epitaxial film, which can be used to explain the mechanism of the influence of the dislocation formation and evolution. One of the effective means of size and density, therefore, the thickness of the nucleation layer can significantly influence the crystal mass of the GaN film.2. The effect of the thickness of the nucleation layer on the crystal quality of the GaN film grown on a graphic sapphire substrate is studied. The scanning electron microscope (SEM) and hrxrd results show that the position of the nucleation point in the three-dimensional growth process is on the crystal of the GaN film. The body mass has an obvious effect. When the position of the three-dimensional growth nucleation point is in the side wall of the figure, it is not conducive to the improvement of the crystal quality of the GaN film, which is due to the difference in the crystal orientation of the nucleated Island grown on the side wall; the position of the three dimensional growth nucleation point is favorable for obtaining high quality GaN crystals when the space of the shape of the nucleation point is in the shape of the shape. The crystal orientation is the same, the growth of the GaN surface is more smooth and the crystal quality is higher. The thickness of the nucleation layer can affect the position of the nucleation point significantly. Therefore, it has an important influence on the crystal quality of Gan,.3, explaining the high carrier mobility in the light Si doped Gan and the strong physical mechanism of the intensity of the yellow band luminescence peak. The results show that the carrier is the carrier. The migration rate increases first and then decreases with the increase of carrier concentration, which is derived from the shielding of the ionization impurity to the dislocation scattering and the enhancement of the ionizing impurity scattering. Under the low doping concentration (the carrier concentration is 2.37 * 1017cm-3), the shielding effect of the ionized impurity to the dislocation scattering is leading. At a high doping concentration (the carrier concentration is 9.73 x 1018cm-3), the enhancement of the ionized impurity scattering leads to the decrease of the carrier mobility. High mobility leads to the increase in the diffusion length of the unbalanced carrier, which causes more defects to participate in the complex, leading to the yellow band luminescence peak intensity of the light Si doped Gan. The effect of mg/ga on the photoelectric performance of P Gan is studied. The result shows that when the mg/ga ratio is 2%, the P type Gan can obtain the highest hole concentration of 4.2 x 1017cm-3. when the mg/ga ratio exceeds 2%, and it will form a mgga-vn that is located in the deep donor level. At this time, the 440nm blue light summit appears, and as the mg/ga ratio is not. At the same time, the blue light peak of 440nm increases gradually. At the same time, the larger Mg/Ga ratio leads to the appearance of granular material on the surface of the P type GaN, and the size of the particles increases with the increase of the ratio. The result shows that the Mg impurity is not all in the main state under the heavy doping state, but a part is.5 in the deep donor state, and the well is studied in the well. The effect of layer thickness on the performance of blue light InGaN/GaN quantum well shows that with the same excitation power, with the increase of the well thickness, the luminescent wavelength of photoluminescence spectrum (PL) appears red shift, and the greater the excitation power, the weaker the degree of red shift. With the increase of the well thickness, the red shift of the PL luminescence wavelength is from the band gap for the thinner quantum well (1.8 and 2.7 nm). For the thicker quantum wells (3.6 and 4.5 nm), the red shift of the PL luminescence wavelength is caused by the shielding effect of the polarization field. The thinnest well sample (1.8 nm) has the highest luminescence intensity because of its weakest polarization effect, but its luminescence wavelength is only 430 nm, which is 20 nm. than the standard blue light wavelength (450 nm). The luminescence wavelength can be reduced to 450 nm by reducing the growth temperature or increasing the flow rate of the In source, but the crystal quality will become worse, which leads to the lower EL luminescence intensity than the 2.7 nm well thickness. Therefore, the standard blue band 2.7 nm is an ideal well thickness.6. The growth rate of the potential well layer in the quantum well is studied on the green InGaN/GaN quantum well. The effect of.HRXRD shows that with the increase of the growth rate of the potential well layer, the interfacial mass of the quantum well is deteriorating.AFM results. The results show that the crack in the quantum well surface begins to appear with the increase of the growth rate of the well layer, and the size of the crack increases gradually.PL results show that the luminescence intensity of PL will be obviously increased at low growth rate, FWH M is narrower and the luminescence wavelength is blue shift. The above results show that the reduction of the growth rate of the quantum well makes the distribution of In components more uniform in the potential well, which is beneficial to obtaining a steep quantum well interface and a more smooth quantum well surface.
【學(xué)位授予單位】：太原理工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TB383.2

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