利用金属键合和激光剥离技术制备GaN/metal /Si异质结构的研究

利用金属键合和激光剥离将生长在蓝宝石衬底上的GaN薄膜转移到Si衬底上。键合后采用波长为248nm的准分子脉冲激光辐照蓝宝石衬底,低温处理去除蓝宝石衬底。系统地研究不同键合温度和激光能量密度对GaN结构和光学特性的影响。AFM、XRD和PL测试表明：键合温度和激光剥离的能量密度较低,转移衬底后GaN的质量较好;激光剥离的阈值能量密度为300mJ/cm2;键合温度400℃的样品均方根粗糙度（RMS）约为50nm。     

激光剥离技术中GaN材料温度场的研究

对使用脉冲激光实现GaN/Sapphire剥离技术,建立了激光剥离过程中GaN外延层一维热传导理论模型。计算分析了单脉冲辐照时,激光剥离过程中GaN外延层内的温度场分布。得到实现激光剥离阈值能量密度为400mJ/cm2,脉冲频率上限约为1400Hz,阈值条件下剥离过程中高温区分布限制在100nm以内。从而证明GaN基发光二极管(LED)外延结构无损伤激光剥离的可行性,并且为激光剥离技术参数的选取提供了理论依据。     

激光剥离技术实现GaN薄膜从蓝宝石衬底移至Cu衬底

在GaN薄膜表面电镀厚100μm的、均匀的金属铜作为转移衬底.采用激光剥离技术,在400mJ/cm2脉冲激光能量密度条件下,成功地将GaN薄膜从蓝宝石衬底转移至Cu衬底.激光剥离后Cu衬底上GaN薄膜的扫描电子显微镜(SEM)测试结果表明,电镀Cu衬底与GaN之间形成致密的结合,对GaN薄膜起到了很好的支撑作用.同时铜的延展性好,使得GaN薄膜内产生的应力得到有效释放,保持了剥离后GaN薄膜的完整性.激光剥离后GaN表面残留物的X射线光电子能谱(XPS)分析显示,激光辐照产生的金属Ga部分与空气中的氧结合形成Ga2O3,这是剥离后GaN表面后处理困难的原因,并给出了相应的解决方法.     

2×25.4mm GaN LED外延膜的激光剥离及其衬底的重复利用

利用激光剥离技术实现直径为50.8mm GaNLED外延膜的大面积完整剥离。激光剥离后的原子力显微镜（AFM）扫描和X射线双晶衍射谱（XRD）表明剥离前后外延膜的质量并未明显改变。并报道了在剥离掉后的蓝宝石（α-Al2O3）衬底上MOCVD外延生长InGaN/GaN多量子阱（MQW′s）LED器件结构,通过光致发光谱（PL）和XRD谱对比分析了在相同条件下剥离掉后衬底与常规衬底上生长的GaNLED外延膜晶体质量。     

2×25.4 mm GaN LED外延膜的激光剥离及其衬底的重复利用

利用激光剥离技术实现直径为50.8 mm CaN LED外延膜的大面积完整剥离.激光剥离后的原子力显微镜(AFM)扫描和X射线双晶衍射谱(XRD)表明剥离前后外延膜的质量并未明显改变.并报道了在剥离掉后的蓝宝石(α-Al2O3)衬底上MOCVD外延生长InGaN/CaN多量子阱(MQW's)LED器件结构,通过光致发光谱(PL)和XRD谱对比分析了在相同条件下剥离掉后衬底与常规衬底上生长的CaN LED外延膜晶体质量.     

蓝宝石上横向外延GaN薄膜

在蓝宝石衬底上利用金属有机物气相外延(MOCVD)方法对横向外延(ELO)GaN薄膜的生长条件进行了研究.在蓝宝石衬底上利用化学腐蚀的方法刻饰出图案,再沉积低温GaN缓冲层作为外延层的子晶层,以降低外延层与衬底的晶格失配与热失配,制备出低位错密度的GaN外延层.分别利用X射线衍射、原子力显微镜及湿法腐蚀对外延层进行检测.     

308nm准分子激光剥离聚酰亚胺薄膜实验研究

为了研究聚酰亚胺薄膜在308nm准分子激光下的剥离效果, 采用实验研究的方法, 分别探究了激光能量密度、光斑重叠率、脉冲频率、衬底温度对激光剥离效果的影响, 并结合显微镜观察剥离后的衬底和薄膜形貌。结果表明, 激光剥离能量阈值约为160mJ/cm2, 在激光能量密度为180mJ/cm2~190mJ/cm2左右、光斑重叠率为68.33%时, 剥离效果较好; 提高衬底温度有利于激光剥离过程。该研究对聚酰亚胺薄膜在柔性电子领域的工业化应用具有一定意义。     

蓝宝石上横向外延GaN薄膜

在蓝宝石衬底上利用金属有机物气相外延(MOCVD)方法对横向外延(ELO)GaN薄膜的生长条件进行了研究.在蓝宝石衬底上利用化学腐蚀的方法刻饰出图案,再沉积低温GaN缓冲层作为外延层的子晶层,以降低外延层与衬底的晶格失配与热失配,制备出低位错密度的GaN外延层.分别利用X射线衍射、原子力显微镜及湿法腐蚀对外延层进行检测.     

利用混合极性制备多孔缓冲层及其在GaN厚膜外延中的应用

使用分子束外延(MBE)技术在(0001)面蓝宝石衬底上生长混合极性的氮化镓(GaN)薄膜,利用不同极性面的GaN薄膜在强碱溶液中腐蚀特性的差异,混和极性样品经腐蚀处理后,得到了一层具有多孔结构的GaN层.以多孔结构的GaN作为缓冲层,用卤化物气相外延(HVPE)方法生长GaN厚膜.X射线双晶衍射和光致发光等测试结果表明,多孔结构的GaN缓冲层可以有效地释放GaN厚膜和衬底之间因热膨胀系数失配产生的应力,使GaN厚膜晶体的质量得到很大提高.     

利用混合极性制备多孔缓冲层及其在GaN厚膜外延中的应用

使用分子束外延(MBE)技术在(0001)面蓝宝石衬底上生长混合极性的氮化镓(GaN)薄膜,利用不同极性面的GaN薄膜在强碱溶液中腐蚀特性的差异,混和极性样品经腐蚀处理后,得到了一层具有多孔结构的GaN层.以多孔结构的GaN作为缓冲层,用卤化物气相外延(HVPE)方法生长GaN厚膜.X射线双晶衍射和光致发光等测试结果表明,多孔结构的GaN缓冲层可以有效地释放GaN厚膜和衬底之间因热膨胀系数失配产生的应力,使GaN厚膜晶体的质量得到很大提高.     

InGaN/GaN和InGaN/AlGaN多量子阱中应变对光致发光特性的影响

对蓝宝石衬底上的InGaN/GaN和InGaN/AlGaN多量子阱结构和经激光剥离去除衬底的InGaN/GaN和InGaN/AlGaN多量子阱结构薄膜样品,进行了光致发光谱、高分辨XRD和喇曼光谱测量.PL测量结果表明,相对于带有蓝宝石衬底的样品,InGaN/GaN多量子阱薄膜样品的PL谱峰值波长发生较小的蓝移,而InGaN/AlGaN多量子阱薄膜样品的PL谱峰值波长发生明显的红移;喇曼光谱的结果表明,激光剥离前后E2模的峰值从569.1减少到567.5cm-1.这说明激光剥离去除衬底使得外延层整体的压应力得到部分释放,但InGaN/GaN与InGaN/AlGaN多量子阱结构中阱层InGaN的应力发生了不同的变化.XRD的结果证实了这一结论.     

Integration of GaN thin films with dissimilar substrate materials by Pd-In metal bonding and laser lift-off

Gallium nitride (GaN) thin films grown on sapphire substrates were successfully bonded and transferred onto GaAs, Si, and polymer “receptor” substrates using a low-temperature Pd-In bond followed by a laser lift-off (LLO) process to remove the sapphire growth substrate. The GaN/sapphire structures were joined to the receptor substrate by pressure bonding a Pd-In bilayer coated GaN surface onto a Pd coated receptor substrate at a temperature of 200°C. X-ray diffraction showed that the intermetallic compound PdIn₃ had formed during the bonding process. LLO, using a single 600 mJ/cm², 38 ns KrF (248 nm) excimer laser pulse directed through the transparent sapphire substrate, followed by a low-temperature heat treatment, completed the transfer of the GaN onto the “receptor” substrate. Cross-sectional scanning electron microscopy and x-ray rocking curves showed that the film quality did not degrade significantly during the bonding and LLO process.     

脉冲Nd:YAG激光器选区晶化制备多晶硅薄膜

采用三倍频后的Nd:YAG固体脉冲激光系统(波长为355 nm)选区诱导晶化非晶硅薄膜,以制备多晶硅薄膜。分别测试了激光晶化前后薄膜的表面形貌和拉曼光谱。在文中分析了400 nm厚薄膜在激光扫描前后的表面形貌变化。拉曼光谱显示薄膜的晶化程度随着激光能量的增加而提高。最优的激光晶化能量密度与薄膜的厚度相关。对于300 nm和400 nm厚的非晶硅薄膜,有效晶化非晶硅的能量密度分别在440-634 mJ/cm²,777-993 mJ/cm²之间。在激光能量密度分别为634 mJ/cm²,975 mJ/cm²和1571 mJ/cm²时,300 nm、400 nm和500 nm厚薄膜达到最好的晶化效果。     

Laser lift-off technique and the re-utilization of GaN-based LED films grown on sapphire substrate

A thin GaN LED film, grown on 2-inch-diameter sapphire substrates, is separated by laser lift-off. Atom force microscopy （AFM） and the double-crystal X-ray diffraction （XRD） have been employed to characterize the performance of Gan before and after the lift-off process. It is demonstrated that the separation and transfer processes do not alter the crystal quality of the GaN films obviously. InGaN/GaN multi-quantum-wells （MQW＇s） structure is grown on the separated sapphire substrate later and is compared with that grown on the conventional substmte under the same condition by using PL and XRD spectrum.     

GaN/metal/Si heterostructure fabricated by metal bonding and laser lift-off

A process methodology has been adopted to transfer GaN thin films grown on sapphire substrates to Si substrates using metal bonding and laser lift-off techniques. After bonding, a single KrF (248 nm) excimer laser pulse was directed through the transparent sapphire substrates followed by low-temperature heat treatment to remove the substrates. The influence of bonding temperature and energy density of the excimer laser on the structure and optical properties of GaN films were investigated systemically. Atomic force microscopy, X-ray diffraction and photolumi-nescence measurements showed that (1) the quality of the GaN film was higher at a lower bonding temperature and lower energy density; (2) the threshold of the energy density of the excimer laser lift-off GaN was 300 mJ/cm~2. The root-mean-square roughness of the transferred GaN surface was about 50 nm at a bonding temperature of 400 ℃.     

A comparative study on the growth of InAlN films on different substrates

This work investigates the growth of InAlN films on Si (111), sapphire (001), GaAs (100) and glass substrates and compares the structural, morphological, electrical and optical properties of these films. One micron thick InAlN films were synthesized on these substrates at 300 °C by using reactive magnetron co-sputtering system. The structural analysis showed the formation of polycrystalline InAlN films on all the substrates having preferred orientation along (101) plane. The films grown on sapphire and silicon displayed better structural quality than the films grown on GaAs and glass. The morphological results revealed identical granular features on all the substrates with small variation in the grain size. The electrical resistivity of InAlN film on sapphire was the lowest one (8×10⁻³ Ω-cm) whereas the highest carrier concentration (8×10²⁰ cm⁻³) was obtained for the film deposited on glass. The energy band gap of InAlN films was determined through UV–vis absorption and reflectance spectroscopy. The band gap value obtained on the glass was slightly higher as compared to its value on the other substrates. The changes in InAlN properties on different substrates were explained on the basis of lattice mismatch, crystallite size, residual strain and orientation of the substrates.     

Crystallization and ablation in annealing of amorphous-Si thin film on glass and crystalline-Si substrates irradiated by third harmonics of Nd:YAG laser

In the present research, an approach of converting amorphous-silicon (a-Si) thin films into polycrystalline thin films using the third harmonics of an all-solid-state pulsed Nd³⁺:YAG laser (355 nm) is studied. Two different samples of a-Si thin films on alkali-free glass (a-Si/glass) substrates and a-Si thin film on crystalline-Si substrates (a-Si/c-Si) are laser treated at different laser fluences ranging from 170 to 960 mJ/cm². The amount of heat incident on the surface has been analyzed theoretically by solving the one-dimensional heat-equation model. The ablation threshold, the region of crystallization and the depth of crystallization have been investigated theoretically. The influence of laser irradiation, ablation and crystallinity has been experimentally analyzed through in-situ reflectivity measurements, scanning electron microscopy (SEM) and Raman spectroscopy studies. In the case of a-Si/c-Si, the extent of crystallinity and the influence of structural characteristics on electronic properties are studied using the Hall-effect technique. The ablation threshold and the range of crystallization regime are in good agreement with the theoretical results. Laser fluence between 300 and 500 mJ/cm² is required for crystallization and the ablation threshold is estimated to be above 500 mJ/cm² for a-Si thin film with a thickness up to 400 nm.     

MOCVD生长的全组分InGaN材料

利用金属有机物化学气相淀积(MOCVD)方法在C面蓝宝石衬底上制备了全组分InGaN薄膜,通过改变生长温度和In/Ga比例成功调控了InGaN合金组分和带隙宽度。利用不同的物理表征手段系统研究了InGaN薄膜的晶体结构和光电学性质,XRD和Hall等测试结果表明:富Ga的InGaN薄膜具有较好的晶体质量,背景电子浓度基本均比富In的InGaN低一个数量级。同时,结合光致发光谱和光学透射谱研究了InGaN合金带隙随In组分的变化关系。