掺C高阻GaN的MOCVD外延生长

利用金属有机物化学气相沉积(MOCVD)技术在蓝宝石衬底上制备了Ga N∶C薄膜。为得到高阻(或半绝缘)的Ga N薄膜,研究了源(CCl4)流量和载气对MOCVD外延Ga N薄膜电学性能的影响,发现CCl4流量和载气对实现高阻的Ga N影响很大。当Ga N缓冲层采用N2作为载气,CCl4的流量为0.016μmol/min时成功实现了Ga N的高阻生长,样品A2的方块电阻高达2.8×107Ω/sq。经原子力显微镜(AFM)测试显示,样品的表面形貌较好,粗糙度均在0.3 nm附近,说明C掺杂对外延Ga N薄膜的表面形貌没有大的影响。低温荧光光谱测试显示黄光峰与刃型位错有关。     

硅基氧化锌薄膜中的发光和复合中心

报道了用MOCVD方法制备的硅基ZnO薄膜中的中性施主-价带D0h发光.ZnO/p-Si结构经空气中700 ℃退火1h,然后进行X射线衍射(XRD)、光致发光(PL)谱和I-V特性测量.实验得到不同载气流量制备的样品都具有整流特性.深能级瞬态谱(DLTS)测量探测到各样品中存在两个施主深能级E1和E2.相应的室温PL谱测量显示样品近带边发射包含不同的发光线.利用高斯拟合方法,样品S2a的PL谱分解为三条发光线b,c和d,其中发光线b可归结为ZnO中的激子发射;DLTS测量得到的施主能级E1与发光线c和d的局域态电离能Ed相关,为D0h中心.此外,实验揭示E2能级的相对隙态密度与PL谱的发光强度成反比,表明深能级E2具有复合中心性质.     

硅基氧化锌薄膜中的发光和复合中心

报道了用MOCVD方法制备的硅基ZnO薄膜中的中性施主-价带D0h发光.ZnO/p-Si结构经空气中700 ℃退火1h,然后进行X射线衍射(XRD)、光致发光(PL)谱和I-V特性测量.实验得到不同载气流量制备的样品都具有整流特性.深能级瞬态谱(DLTS)测量探测到各样品中存在两个施主深能级E1和E2.相应的室温PL谱测量显示样品近带边发射包含不同的发光线.利用高斯拟合方法,样品S2a的PL谱分解为三条发光线b,c和d,其中发光线b可归结为ZnO中的激子发射;DLTS测量得到的施主能级E1与发光线c和d的局域态电离能Ed相关,为D0h中心.此外,实验揭示E2能级的相对隙态密度与PL谱的发光强度成反比,表明深能级E2具有复合中心性质.     

GaN基光发射二极管中深能级研究

利用深能级瞬态谱 (DLTS)仪对 Si C衬底上 Ga N基光发射二极管 (LED)中 n-In0 .2 5Ga0 .75N层的深能级进行了研究。在 77K到 3 0 0 K的温度扫描范围内只测量到一个 DLTS峰。该 DLTS峰在反向偏压为 3 V时有一极大值 ,说明 n-In0 .2 5Ga0 .75N层此时全部被耗尽。改变测量的率窗 ,得到该深能级在导带下 0 .2 4e V处 ,浓度为 2 .2 % ND,俘获截面为 1 .93× 1 0 - 1 5cm2。在 Ga N材料中 ,其他小组也报道了此位置上的深能级结果。结合文中的工作 ,该深能级可能和 n-In0 .2 5Ga0 .75N层中的线位错有关。     

Mn~+离子注入的GaN薄膜的光学性质及其磁性

利用离子注入法将磁性离子Mn+注入到采用金属有机化学气相沉积法制备的Ga N薄膜中,获得了稀磁半导体(Ga,Mn) N.光致发光谱结果显示由于Mn的注入,使Ga N中常见的黄带发射被大大抑制.在反射和吸收光谱中,观察到锰引入的新吸收带,分析表明该带是由电荷转移过程和锰引入能级(价带顶上310 m e V处)的吸收组成的.透射光谱显示(Ga,Mn) N的光学带隙发生了红移,计算表明该红移量为30±5 m e V.震动样品磁强计的测量结果证实了Mn掺杂的Ga N样品在室温下具有铁磁性.     

氮化镓注镁(Mg:GaN)的光致发光

利用低压MOCVD在蓝宝石衬底上外延生长了GaN,用离子注入法掺入Mg杂质,退火后,进行光致发光测量,观察到显著的蓝光发射和黄带发射.光谱分析给出了与注入Mg离子相关的GaN禁带中能级的精细结构,其中: 间位Mg(Mgi)能级(导带下170meV)到替位Mg(MgGa)受主能级(价带上250meV)的跃迁产生了415nm发光峰; 该能级到价带上390meV能级的跃迁,以及带有紧邻N空位的替位Mg(MgGaVN)能级(导带下310meV)到 MgGa受主能级的跃迁,均产生了438nm发光峰.另外,退火使GaN晶格结构部分恢复,再现了黄带发射.     

氮化镓注镁(Mg:GaN)的光致发光

利用低压MOCVD在蓝宝石衬底上外延生长了GaN,用离子注入法掺入Mg杂质,退火后,进行光致发光测量,观察到显著的蓝光发射和黄带发射.光谱分析给出了与注入Mg离子相关的GaN禁带中能级的精细结构,其中: 间位Mg(Mgi)能级(导带下170meV)到替位Mg(MgGa)受主能级(价带上250meV)的跃迁产生了415nm发光峰; 该能级到价带上390meV能级的跃迁,以及带有紧邻N空位的替位Mg(MgGaVN)能级(导带下310meV)到 MgGa受主能级的跃迁,均产生了438nm发光峰.另外,退火使GaN晶格结构部分恢复,再现了黄带发射.     

制备参数和后处理对ZnO薄膜光学性质的影响

采用脉冲激光沉积技术在不同生长气氛氧压(10-3pa1、0-2Pa、10-1Pa、1Pa、10Pa)和生长衬底温度(250~600℃)下制备了高度c轴取向的ZnO薄膜。光致发光(PL)光谱表明,氧压和衬底温度对ZnO的光学性质有重要影响。制备紫外(UV)发射强的ZnO薄膜,要综合考虑氧压和衬底温度两个参数,衬底温度升高,氧气氛压强要相应升高。进一步研究表明,在化学配比失衡的情况下,升高衬底温度和退火会在ZnO中产生缺陷和杂质束缚电子态,束缚电子态引起的晶格弛豫使局域电子态发生多声子无辐射跃迁,ZnO深能级发射由辐射复合变为无辐射复合。     

Mn+离子注入的GaN薄膜的光学性质及其磁性

利用离子注入法将磁性离子Mn+注入到采用金属有机化学气相沉积法制备的GaN薄膜中,获得了稀磁半导体(Ga,Mn)N.光致发光谱结果显示由于Mn的注入,使GaN中常见的黄带发射被大大抑制.在反射和吸收光谱中,观察到锰引入的新吸收带,分析表明该带是由电荷转移过程和锰引入能级(价带顶上310meV处)的吸收组成的.透射光谱显示(Ga,Mn)N的光学带隙发生了红移,计算表明该红移量为30±5meV.震动样品磁强计的测量结果证实了Mn掺杂的GaN样品在室温下具有铁磁性.     

MOCVD生长的InGaN薄膜中的相分离

利用X射线衍射(XRD)测量用MOCVD生长的In Ga N样品,观察到In N相.通过X射线衍射理论,计算得到In N相在In Ga N中的含量.通过退火和变化生长条件发现In N相在In Ga N薄膜中的含量与生长时N2 载气流量、反应室压力和薄膜中存在的应力有关.进一步的分析表明In Ga N合金中出现In N相的主要原因是相分离.     

Effect of gas feeding methods on optical properties of GaN grown by rapid thermal chemical vapor deposition reactor

The origin of the radiative recombination leading to yellow luminescence (YL) has been elucidated by the study of luminescence properties of GaN films grown with two different gas feeding methods. GaN films were grown on a (0001) sapphire substrate in a rapid thermal chemical vapor deposition (RTCVD) reactor. GaN films emitted two different luminescence energies, 2.2 and 3.47 eV, depending on the introducing position of hydrogen gas in the growth reactor. The distribution of the TMGa flow and gas phase reactions in the reactor were investigated to understand the effect of the gas feeding methods on the optical properties of GaN films. The results suggest that YL is related to Ga vacancies in the grown films.     

Hydrogen Induced Yellow Luminescence in GaN Grown by Halide Vapor Phase Epitaxy

Strong yellow luminescence (YL) was found in GaN grown by the halide vapor phase epitaxy technique, using an NH₃-HCl-GaCl-N₂-H₂ growth chemistry. The low-temperature (less than 100K) thermal activation energy of the yellow luminescence was determined to be ∼18 meV, which indicates that a shallow donor, rather than a ‘shallow’ acceptor, was involved in observed radiative transition. The temperature dependence of the YL peak energy and the shape of the YL band imply that there are multiple recombination channels involved in the YL band. The ratio of integrated intensity of yellow-to-bandedge luminescence decreased with an increase of HCl (and hence GaCl and growth rate) in the growth ambient.     

预处理蓝宝石衬底上生长高质量 GaN 显示薄膜

采用化学方法腐蚀部分 c-面蓝宝石衬底,在腐蚀区域形成一定的图案,利用 LP-MOCVD 在此经过表面处理的蓝宝石衬底上外延生长 GaN 薄膜.采用高分辨率双晶X射线衍射(DCXRD)、光致发光光谱(PL)、透射光谱分析GaN薄膜的晶体质量和光学质量.分析结果表明,CaN 薄膜透射谱反映出的 CaN 质量与 X射线双晶衍射测量的结果一致,即透射率越大,半高宽越小,结晶质量越好;对蓝宝石衬底进行前处理可以大大改善GaN薄膜的晶体质量和光学质量,其(0002)面及(1012)面XRD半高宽(FWHM)分别降低到 208.80arcsec 及 320.76arcsec,而且其光致发光谱中的黄光带几乎可以忽略.     

Si离子注入和退火温度对GaN黄光的影响

对光致发光谱中无黄光和有强黄光的两组GaN样品作了Si离子注入 ,研究了Si离子注入及退火温度对其黄光的影响 .当退火温度升高时 ,不管是哪一组样品 ,其黄光强度和黄光强度与带边发光带强度之比都是增强的 .无黄光的GaN样品在注入Si离子并经退火后出现明显的黄光 ;而有强黄光的GaN样品经相同处理后 ,其黄光强度较原生样品大大降低 .实验结果表明离子注入加上适当退火会在GaN中引入与黄光有关的深受主缺陷从而使黄光强度增加 ,此外 ,在离子注入过程中GaN表面不仅可以吸附离子注入引入的点缺陷 ,而且还能够吸附GaN中原有的与黄光有关的点缺陷 ,这种吸附作用随离子注入剂量增加而变强 .     

HVPE生长的高质量GaN纳米柱的光学性能

GaN纳米材料因具有优异的晶体质量和突出的光学性能及发射性能,日益受到关注.研究了一种利用氢化物气相外廷(HVPE)系统生长高质量的GaN纳米柱的方法.使用镍作为催化剂,在蓝宝石衬底上生长出了GaN纳米柱.在不同生长时间和不同HC1体积流量下制备了多组样品,使用扫描电子显微镜(SEM)、X射线衍射(XRD)和光致发光(PL)谱对样品进行了分析表征.测试结果表明,在较低的HC1体积流量下,生长2 min的样品具有较高的晶体质量和较好的光学性质.讨论了不同生长阶段的GaN纳米结构发光特性的变化规律,认为纳米结构所产生的表面态密度大小差异会造成带边峰位的红移和展宽.     

生长压力对GaN材料光学与电学性能的影响

研究了采用MOCVD技术分别在100与500Torr反应室压力下生长的非故意掺杂GaN薄膜的光学与电学性能。研究表明,低压100Torr外延生长条件可以有效地降低Ga与NH3气相反应造成GaN薄膜的碳杂质沾污,从而抑制造成光致发光中黄光峰与蓝光峰的深受主的形成,所制备的材料表现出较好的光学性能。同时,不同生长压力下的GaN薄膜表现出相异的电学性能,即在500Torr下生长的样品通常表现出更高的载流子浓度（（4.6-6.4）×1016 cm-3）与更高的迁移率（446-561cm2/（V.s））,而100Torr下生长的样品通常表现为更低的载流子浓度（1.56-3.99）×1016 cm-3与更低迁移率（22.9-202cm2/（V.s））。     

Influence of oxygen flow rate on microstructural,electrical and optical properties of indium tin tantalum oxide films

Indium tin oxide (ITO) and indium tin tantalum oxide (ITTO) films were deposited on glass substrates by magnetron sputtering technology with one or two targets. Properties of ITO and ITTO films deposited at different oxygen flow rates were contrastively studied. Ta-doping strengthens along the orientation of (400) plane and leads to better crystalline structure as well as to a decrease in surface roughness. The increase in oxygen flow rate increases sheet resistance and reduces carrier concentration, and ITTO films show higher carrier concentration. Certain oxygen flow rates can improve the visible light transmittance of films, but excessive oxygen can worsen the optical properties. The carrier concentration has an important influence on near-IR reflection, near-UV absorption and optical band gap. The optical band gap decreases with the increasing of oxygen flow rate, and ITTO films show wider optical band gap than ITO films. ITTO films prepared by co-sputtering reveal better optical–electrical properties and chemical and thermal stability than ITO films.     

Analysis of defect related optical transitions in biased AlGaN/GaN heterostructures

The optical transitions in AlGaN/GaN heterostructures that are grown by metalorganic chemical vapor deposition (MOCVD) have been investigated in detail by using Hall and room temperature (RT) photoluminescence (PL) measurements. The Hall measurements show that there is two-dimensional electron gas (2DEG) conduction at the AlGaN/GaN heterointerface. PL measurements show that in addition to the characteristic near-band edge (BE) transition, there are blue (BL) and yellow luminescence (YL) bands, free-exciton transition (FE), and a neighboring emission band (NEB). To analyze these transitions in detail, the PL measurements were taken under bias where the applied electric field changed from 0 to 50 V/cm. Due to the applied electric field, band bending occurs and NEB separates into two different peaks as an ultraviolet luminescence (UVL) and Y₄ band. Among these bands, only the yellow band is unaffected with the applied electric field. The luminescence intensity change of these bands with an electric field is investigated in detail. As a result, the most probable candidate of the intensity decrease with an increasing electric field is the reduction in the radiative lifetime.     

Flow modulation epitaxy of indium gallium nitride

InGaN layers were grown on GaN films by flow modulation epitaxy (FME) using the precursors trimethylgallium, trimethylindium, and ammonia. The indium composition of the FME grown layers was generally lower than of films grown under the same conditions in the continuous growth mode, but which had been of poor optical quality. The indium incorporation efficiency increased with decreasing ammonia flush time, increasing ammonia flow during group-III injection, and increasing group-III precursor injection time. Films grown under optimized conditions showed intense band edge related luminescence at room temperature up to a wavelength of 465 nm. Atomic force microscopy investigations revealed a strong dependence of the surface morphology of the InGaN films on the growth mode.     

Influence of AlGaN deep level defects on AlGaN/GaN 2-DEG carrierconfinement

We have used low energy electron-excited nanoscale luminescence spectroscopy (LEEN) to detect the defects in each layer of AlGaN/GaN HEMT device structures and to correlate their effect on two-dimensional electron gas (2-DEG) confinement. We investigated AlGaN/GaN heterostructures with different electrical properties using incident electron beam energies of 0.5 to 15 keV to probe electronic state transitions within each of the heterostructure layers. AlGaN heterostructures of 25 nm thickness and nominal 30% Al concentration grown on GaN buffer layers on sapphire substrates by plasma-assisted molecular beam epitaxy exhibited a range of polarization-induced electron densities and room temperature mobilities. In general, the spectra exhibit AlGaN band edge emission at ~3.8 eV or ~4.0 eV, GaN band edge emission at ~3.4 eV, yellow luminescence (YL) features at 2.18 eV and 2.34 eV, and a large emission in the infrared (<1.6 eV) from the GaN cap layer used to passivate the AlGaN outer surface. These heterostructures also show high strain in the 2 nm-thick GaN layer with evidence for a Franz-Keldysh red shift due to piezoelectric charging. The LEEN depth profiles reveal differences between the structures with and without 2-DEG confinement and highlight the importance of AlGaN defects in the near 2-DEG region