GaN基LED不同功能层的MOCVD生长及其性能研究

发布时间：2018-06-21 20:45

本文选题：发光二极管 + GaN　；参考：《太原理工大学》2016年博士论文

【摘要】：LED作为第三代光源,具有节能、环保、寿命长、稳定性高、体积小等优点,可以广泛应用于各种指示、显示、装饰、背光源和固态照明等领域。自中村修二成功制备了宽禁带GaN基半导体材料之后,具有商业应用价值的蓝光LED获得实现,LED在光效提升和成本降低方面取得了飞速的发展。但LED仍有一些问题需要进一步解决和完善,例如,外延生长参数对GaN晶体质量的影响机制还不明确;高空穴浓度低电阻率p型GaN的制备困难;InGaN与GaN的物理化学性能差异使得高质量量子阱生长困难等。本论文从以上提出的问题出发,对GaN基LED外延结构各功能层进行生长,探究了工艺参数和结构参数对不同功能层结构性质以及光电性能的影响,并对其影响机制做了深入的分析。具体内容如下:1、研究了形核层厚度(分别为15、25和45 nm)对平面蓝宝石衬底上生长的GaN薄膜晶体质量的影响。高分辨X射线衍射(HRXRD)结果表明:当形核层厚度为25 nm时,GaN外延薄膜的(002)和(102)面的HRXRD谱的半高宽(FWHM)最小,分别为267和284 arcsec。原子力显微镜(AFM)结果表明:形核层退火后,样品表面呈岛状结构。形核层厚度的增加有利于获得大尺寸的岛,但是岛的均匀性较差。尺寸大、均匀性好、密度低的形核岛对GaN外延薄膜的晶体质量是最有利的,这可采用位错的产生和演变机制来解释影响机理。调控形核层厚度是控制岛的尺寸和密度的有效手段之一,因此,形核层厚度能够显著影响gan薄膜的晶体质量。2、研究了形核层厚度对图形蓝宝石衬底上生长的gan薄膜晶体质量的影响。扫描电子显微镜(sem)和hrxrd结果表明:三维生长过程中形核点的位置对gan薄膜的晶体质量有明显的影响,当三维生长形核点的位置处于图形的侧壁时不利于gan薄膜晶体质量的提高,这是由于侧壁上长大的形核岛晶体取向存在差异;三维生长形核点的位置处于图形的间隙时有利于获得高质量的gan晶体,这时形核岛的晶体取向一致,生长的gan表面较平整,晶体质量较高。形核层的厚度能够显著影响形核点的位置,因此其对gan的晶体质量有重要的影响。3、解释了轻si掺杂gan中较高的载流子迁移率以及较强的黄带发光峰强度的物理机制。结果表明:载流子迁移率随着载流子浓度的升高呈现出先增加后降低的变化趋势,这种变化源自于电离杂质对位错散射的屏蔽和电离杂质散射的增强。在低掺杂浓度下(载流子浓度为2.37×1017cm-3),电离杂质对位错散射的屏蔽作用处于主导地位,从而导致迁移率的骤升。在高的掺杂浓度下(载流子浓度为9.73×1018cm-3),电离杂质散射的增强导致载流子迁移率的降低。高的迁移率导致光生非平衡载流子的扩散长度增加,从而引起更多的缺陷参与到复合中去,导致轻si掺杂gan的黄带发光峰强度增强。4、研究了mg/ga比对p型gan光电性能的影响。结果表明:当mg/ga比为2%时,p型gan可以获得最高的空穴浓度4.2×1017cm-3。当mg/ga比超过了2%时,会形成位于深施主能级的mgga-vn,起自补偿作用,此时,440nm的蓝光发光峰会出现,并且随着mg/ga比的不断增大,440nm的蓝光发光峰逐渐增强。同时,较大的Mg/Ga比会导致p型GaN表面出现颗粒状的物质,并且随着比值的增加,颗粒的尺寸增大。结果表明在重掺杂状态下,Mg杂质并不是全部以受主状态存在,而是部分以深施主状态存在。5、研究了阱层厚度对蓝光InGaN/GaN量子阱性能的影响。结果表明:在相同的激发功率下,随着阱厚的增加,光致发光谱(PL)发光波长出现红移,并且激发功率越大,红移程度越弱。随着阱厚的增加,对于较薄的量子阱(1.8和2.7 nm),PL发光波长的红移是由带隙填充效应引起的;对于较厚的量子阱(3.6和4.5 nm),PL发光波长的红移是由极化场屏蔽效应引起的。阱最薄的样品(1.8 nm)由于其极化效应最弱,EL谱具有最高的发光强度,但其发光波长较短仅有430 nm,比标准的蓝光波长(450 nm)蓝移了20 nm。虽然,可以通过降低生长温度或增加In源流量的方法使其发光波长变为450 nm,但其晶体质量会变差,导致EL发光强度比2.7 nm阱厚的样品低,因此,在标准的蓝光波段2.7 nm为较理想的阱厚。6、研究了量子阱中势阱层的生长速率对绿光InGaN/GaN量子阱性能的影响。HRXRD结果表明:随着势阱层生长速率的提高,量子阱的界面质量不断恶化。AFM结果表明:随着阱层生长速率的提高,量子阱表面开始出现裂纹,并且裂纹的尺寸逐渐增大。PL结果表明:在低的生长速率下,PL发光强度会明显提高,FWHM变窄,发光波长蓝移。以上结果表明降低量子阱的生长速率使势阱中In组分分布更均匀,有利于获得陡峭的量子阱界面和较平整的量子阱表面。
[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.
【学位授予单位】：太原理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TB383.2

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