InGaN/GaN多量子阱蓝光LED的p-GaN盖层的MOCVD生长研究

利用金属有机物化学气相淀积（MOCVD）生长了InGaN／GaN多量子阱（MQW）蓝光发光二极管（LED），研究了不同Cp2Mg流量下生长的p-GaN盖层对器件电学特性的影响。结果表明，随着Cp2Mg流量的提高，漏电流升高，并且到达一临界点会迅速恶化；正向压降则先降低，后升高。进而研究相同生长条件下生长的p-GaN薄膜的电学特性、表面形貌及晶体质量，结果表明，生长p-GaN盖层时，Cp2Mg流量过低，盖层的空穴浓度低，电学特性不好；Cp2Mg流量过高，则会产生大量的缺陷，盖层晶体质量与表面形貌变差，使得空穴浓度降低，电学特性变差。因此，生长p-GaN盖层时，为使器件的正向压降与反向漏电流均达到要求，Cp2Mg流量应精确控制。     

蓝宝石衬底的斜切角对GaN薄膜特性的影响

利用金属有机物化学气相沉积技术在具有斜切角度的蓝宝石衬底(0～0.3°)上生长了非故意掺杂GaN薄膜,并采用显微镜、X射线双晶衍射、光荧光及霍尔技术对外延薄膜的表面形貌、晶体质量、光学及电学特性进行了分析.结果表明,采用具有斜切角度的衬底,可以有效改善GaN外延薄膜的表面形貌、降低位错密度、提高GaN的晶体质量及其光电特性,并且存在一个衬底最优斜切角度0.2°,此时外延生长出的GaN薄膜的表面形貌和晶体质量最好.     

InAIN薄膜MOCVD外延生长研究

为了研究不同压力和不同模板对InAlN薄膜外延生长的影响,分别选取以GaN为模板时生长压力为4.00、6.67和13.33 kPa,压力为4.00 kPa时模板为GaN和A1N这两组条件进行实验比较.研究发现,随着生长压力的增加,样品中In含量降低,样品的粗糙度则随压力的增加而增大;压力为4.00 kPa时,分别以摇摆曲线半高宽(FWHM)为86.97”的AIN和224.1”的GaN为模板,发现A1N模板上生长的InAIN样品(002)和(102)峰的FWHM值及表面粗糙度比上述GaN为模板生长的InAlN样品都要小很多.综合以上结果可初步得知:降低压力可以优化InAlN薄膜的表面形貌,增加In组分含量;采用高质量的AIN作模板能生长出晶体质量和表面形貌都比较好的InAlN薄膜.     

Influence of growth conditions on the V-defects in InGaN/GaN MQWs

The influence of the growth temperature,TMIn/TEGa andⅤ/Ⅲratio on the V-defects of InGaN/GaN multi-quantum wells（MQWs） has been investigated and discussed.When the TMIn flow increases from 180 to 200 sccm,the density of V-defects increases from 2.72×10¹⁸ to 5.24×10¹⁸ cm^-2,and the V-defect width and depth increase too.The density also increases with the growth temperature.The densities are 2.05×10⁸,2.72×10¹⁸ and 4.23×10⁸ cm^-2,corresponding to a growth temperature of 748,753 and 758℃respectively.When the NH₃ flows are 5000,6600 and 8000 sccm,the densities of the V-defects of these samples are 6.34×10¹⁸,2.72×10¹⁸ and 4.13×10¹⁸ cm^-2,respectively.A properⅤ/Ⅲratio is needed to achieve step flow growth mode.We get the best quality of InGaN/GaN MQWs at a growth temperature of 753℃TMIn flow at 180 sccm,NH₃ flow at 6600 sccm,a flatter surface and less V-defects density.The depths of these V-defects are from 10 to 30 nm,and the widths are from 100 to 200 nm.In order to suppress the influence of V-defects on reverse current and electro-static discharge of LEDs,it is essential to grow thicker p-GaN to fill the V-defects.     

Improvement of the efficiency droop of GaN-LEDs using an AlGaN/GaN superlattice insertion layer

With an n-AlGaN(4 nm)/GaN(4 nm) superlattice(SL) inserted between an n-GaN and an InGaN/GaN multiquantum well active layer,the efficiency droop of GaN-based LEDs has been improved.When the injection current is lower than 100 mA,the lumen efficiency of the LED with an n-AlGaN/GaN SL is relatively small compared to that without an n-AlGaN/GaN SL.However,as the injection current increases more than 100 mA,the lumen efficiency of the LED with an n-AlGaN/GaN SL surpasses that of an LED without an n-AlGaN/GaN SL. The wall plug efficiency of an LED has the same trend as lumen efficiency.The improvement of the efficiency droop of LEDs with n-AlGaN/GaN SLs can be attributed to a decrease in electron leakage due to the enhanced current spreading ability and electron blocking effect at high current densities.The reverse current of LEDs at -5 V reverse voltage decreases from 0.2568029 to 0.0070543μA,and the electro-static discharge(ESD) pass yield of an LED at human body mode(HBM)-ESD impulses of 2000 V increases from 60%to 90%.     

插入n-AlGaN/GaN超晶格改善GaN基LED的droop效应

在GaN基LED的n-GaN和InGaN/GaN发光区之间插入n-AlGaN/GaN超晶格来改善其droop效应。注入电流低于100mA时,插入n-AlGaN/GaN超晶格的LED的流明效率低于没有插入层的LED。注入电流高于100mA时,插入n-AlGaN/GaN超晶格的LED的流明效率高于没有插入层的LED。插入n-AlGaN/GaN超晶格后,GaN基LED在-5V的反向电压下,漏电由2.568029μA减少到0.070543μA。人体模式下,插入n-AlGaN/GaN超晶格的LED在2000V的静电电压下的通过率从60%提高到了90%。LED droop效应的改善是因为n-AlGaN/GaN超晶格过滤了穿透位错并改善了电流扩展能力。     

P 型氮化镓层生长压力对InGaN/GaN基发光二极管性能的影响

The advantages of In Ga N/Ga N light emitting diodes(LEDs) with p-Ga N grown under high pressures are studied.It is shown that the high growth pressure could lead to better electronic properties of p-Ga N layers due to the eliminated compensation effect.The contact resistivity of p-Ga N layers are decreased due to the reduced donor-like defects on the p-Ga N surface.The leakage current is also reduced,which may be induced by the better filling of V-defects with p-Ga N layers grown under high pressures.The LED efficiency thus could be enhanced with high pressure grown p-Ga N layers.     

MOCVD于高温AlN模板上生长的AlGaN材料

A high temperature AlN template was grown on sapphire substrate by metalorganic chemical vapor deposition.AFM results showed that the root mean square of the surface roughness was just 0.11 nm.Optical transmission spectrum and high resolution X-ray diffraction（XRD）characterization both proved the high quality of the AlN template.The XRD（002）rocking curve full width at half maximum（FWHM）was about 53.7 arcsec and（102）FWHM was about 625 arcsec.The densities of screw threading dislocations（TDs）and edge TDs wereestimated to be - 6 × 10^6 cm^-2 and - 4.7 ×10^9 cm^-2. AlGaN of Al composition 80.2% was further grown on the AlN template. The RMS of the surface roughness was about 0.51 nm. XRD reciprocal space mapping was carried out to accurately determine the Al composition and relaxation status in the AlGaN epilayer. The XRD （002） rocking curve FWHM of the AIGaN epilayer was about 140 arcsec and （102） FWHM was about 537 arcsec. The density of screw TDs was estimated to be - 4 × 10^7 cm^-2 and that of edge TDs was - 3.3 × 10^9 cm^-2. These values all prove the high quality of the AlN template and AlGaN epilayer.     

生长停顿改善MOCVD生长InGaN/GaN多量子阱的特性

利用金属有机物化学气相淀积(MOCVD)生长了InGaN/GaN多量子阱(MQWs)结构,研究了生长停顿对InGaN/GaN MQWs特性的影响.结果表明,采用生长停顿,可以改善MQWs界面质量,提高MQWs的光致发光(PL)与电致发光(EL)强度;但生长停顿的时间过长,阱的厚度会变薄,界面质量变差,不仅In组分变低,富In的发光中心减少,而且会引入杂质,致使EL强度下降.     

InAlN薄膜MOCVD外延生长研究

为了研究不同压力和不同模板对InA lN薄膜外延生长的影响,分别选取以GaN为模板时生长压力为4.00、6.67和13.33 kPa,压力为4.00 kPa时模板为GaN和A lN这两组条件进行实验比较。研究发现,随着生长压力的增加,样品中In含量降低,样品的粗糙度则随压力的增加而增大;压力为4.00 kPa时,分别以摇摆曲线半高宽(FWHM)为86.97″的A lN和224.1″的GaN为模板,发现A lN模板上生长的InA lN样品(002)和(102)峰的FWHM值及表面粗糙度比上述GaN为模板生长的InA lN样品都要小很多。综合以上结果可初步得知:降低压力可以优化InA lN薄膜的表面形貌,增加In组分含量;采用高质量的A lN作模板能生长出晶体质量和表面形貌都比较好的InA lN薄膜。