线性分布的In组分对紫色InGaN/GaN单量子阱发光特性的影响

采用数值模拟的方法研究了具有相同的平均In组分,但In组分的分布不同的3个紫色InGaN/GaN单量子阱样品的光谱特性.通过分析样品的电致发光谱、能带结构、波函数交叠以及载流子浓度分布等,发现沿生长方向阱内In组分线性增加的单量子阱样品的发光效率最高,而In组分线性减小的样品发光效率最低.这是因为In组分的线性增加能够减弱极化场对价带的影响,使阱内价带变得更加平缓.这不仅降低了空穴的注入势垒高度、增大了阱中的空穴浓度,还增强了阱内电子-空穴波函数的交叠积分,提高了辐射复合几率,从而使In组分线性增加的量子阱的发光效率显著提高.     

ZnCdSe量子阱/CdSe量子点耦合结构中的激子复合

采用MOCVD方法制备了ZnCdSe量子阱/CdSe量子点耦合结构,利用低温(5K)光致发光光谱和变密度发光光谱研究了该结构中的激子隧穿和复合.观察到在该结构中存在由量子阱到量子点的激子隧穿现象.改变垒层厚度会对量子阱和量子点的发光产生显著影响.在垒层较薄的阱/点耦合结构中,隧穿效应可以有效地抑制量子阱中的带填充和饱和效应.     

ZnCdSe量子阱/CdSe量子点耦合结构中的激子复合

采用MOCVD方法制备了ZnCdSe量子阱/CdSe量子点耦合结构,利用低温(5K)光致发光光谱和变密度发光光谱研究了该结构中的激子隧穿和复合. 观察到在该结构中存在由量子阱到量子点的激子隧穿现象. 改变垒层厚度会对量子阱和量子点的发光产生显著影响. 在垒层较薄的阱/点耦合结构中,隧穿效应可以有效地抑制量子阱中的带填充和饱和效应.     

红橙光InGaN/GaN量子阱的结构与光学性质研究

采用金属有机物化学气相沉积(MOCVD)技术生长了具有高In组分InGaN阱层的InGaN/GaN多量子阱(MQW)结构,高分辨X射线衍射(HRXRD)ω-2θ扫描拟合得到阱层In含量28%。比较大的表面粗糙度表明有很大的位错密度。室温下光致荧光(PL)研究发现该量子阱发射可见的红橙光,峰位波长在610 nm附近。变温PL(15～300 K)进一步揭示量子阱在低温下有两个发光机制,对应的发射峰波长分别为538 nm和610 nm。由于In分凝和载流子的局域化导致的载流子动力改变,使得量子阱PL发光峰值随温度增加呈明显的"S"变化趋势。     

InGaAs/GaAs量子阱中自组装InAs量子点的光学性质

在InGaAs/GaAs量子阱中生长了两组InAs量子点样品,用扫描电子显微镜(SEM)测量发现,量子点呈棱状结构,而不是通常的金字塔结构,这是由多层结构的应力传递及InGaAs应变层的各向异性引起的.采用变温光致发光谱(TDPL)和时间分辨谱(TRPL)研究了其光致发光稳态和瞬态特性.研究发现,InGaAs量子阱层可以有效地缓冲InAs量子点中的应变,提高量子点的生长质量,可以在室温下探测到较强的发光峰.在量子阱中生长量子点可以获得室温下1 318 nm的发光,并且使其PL谱的半高宽减小到25 meV.     

掺Si对AlGaInP/GaInP多量子阱发光性能的影响

研究了Si掺杂对MOCVD生长的(Al0.3Ga0.7)In0.5P/Ga0.5In0.5P多量子阱发光性能的影响.样品分为两类:一类只生长了(Al0.3Ga0.7)In0.5P/Ga0.5In0.5P多量子阱结构;另一类为完整的多量子阱LED结构.对于只生长了(Al0.3Ga0.7)In0.5P/Ga0.5In0.5P多量子阱结构的样品,掺Si没有改变量子阱发光波长,但使得量子阱发光强度略有下降,发光峰半高宽明显增大.这应是掺Si使量子阱界面质量变差导致的.而在完整LED结构的情况下,掺Si却大大提高了量子阱的发光强度.相对于未掺杂多量子阱LED结构,垒层掺Si使多量子阱的发光强度提高了13倍,阱层和垒层均掺Si使多量子阱的发光强度提高了28倍,并对这一现象进行了讨论.     

掺Si对AlGaInP/GaInP多量子阱发光性能的影响

研究了Si掺杂对MOCVD生长的（Al0.3Ga0.7）In0.5P/Ga0.5In0.5P多量子阱发光性能的影响．样品分为两类：一类只生长了（Al0.3Ga0.7）In0.5P/Ga0.5In0.5P多量子阱结构;另一类为完整的多量子阱LED结构．对于只生长了（Al0.3Ga0.7）In0.5P/Ga0.5In0.5P多量子阱结构的样品,掺Si没有改变量子阱发光波长,但使得量子阱发光强度略有下降,发光峰半高宽明显增大．这应是掺Si使量子阱界面质量变差导致的．而在完整LED结构的情况下,掺Si却大大提高了量子阱的发光强度．相对于未掺杂多量子阱LED结构,垒层掺Si使多量子阱的发光强度提高了13倍,阱层和垒层均掺Si使多量子阱的发光强度提高了28倍,并对这一现象进行了讨论．     

组合多量子阱的发光特性研究

通过在７７Ｋ时对ＺｎＣｄＳｅ－ＺｎＳｅ组合多量子阱结构的发光特性的测量,我们观测到了分别来自两组量子阱的激子发光,其跃迁能量与采用包络函数法计算的结果相符。由于两组量子阱之间注入效应的存在,使得两组量子阱在变密度激发和时间分辨光谱中表现出不同的发光特性。     

氢离子注入法提高InAsP/InP应变多量子阱发光特性

采用气态源分子束外延系统生长了InAsP/InP应变多量子阱,研究了H 注入对量子阱光致发光谱的影响以及高温快速退火对离子注入后的量子阱发光谱的影响.发现采用较低H 注入能量(剂量)时,量子阱发光强度得到增强;随着H 注入能量(剂量)的增大,量子阱发光强度随之减小.H 注入过程中,部分隧穿H 会湮灭掉量子阱结构界面缺陷,同时H 也会对量子阱结构带来损伤,两者的竞争影响量子阱发光强度的变化.高温快速退火处理后,离子注入后的量子阱样品发光峰位在低温10K相对于未注入样品发生蓝移,蓝移量随着H 注入能量或剂量的增大而增加.退火过程中缺陷扩散以及缺陷扩散导致的阱层和垒层之间不同元素互混是量子阱发光峰位蓝移的原因.     

合金无序和界面不平整对InGaAs/GaAs应变量子阱光谱展宽的影响

用光荧光和光吸收的实验方法研究了InGaAs/GaAs应变量子阱低温下的光谱展宽机理。实验观察到激子谱线半宽随着InGaAs层厚度和In的组分增加而增大。采用有效晶体近似的方法分析了实验数据,发现样品中合金组合无序引起的激子谱线展宽是主要的光谱展宽机理。实验中还发现与轻空穴有关的吸收光谱结构在升温过程中由吸收峰变为台阶状的谱结构。该现象可用与轻空穴有关的吸收为空间间接跃过来解释。     

Structural and optical investigation of InGaN/GaN multiple quantum well structures with various indium compositions

We have studied the influence of indium (In) composition on the structural and optical properties of In_x Ga_1−xN/GaN multiple quantum wells (MQWs) with In compositions of more than 25% by means of high-resolution x-ray diffraction (HRXRD), photoluminescence (PL), and transmission electron microscopy (TEM). With increasing the In composition, structural quality deterioration is observed from the broadening of the full width athalf maximum of the HRXRD superlattice peak, the broad multiple emission peaks oflow temperature PL, and the increase of defect density in GaN capping layers and InGaN/GaN MQWs. V-defects, dislocations, and two types of tetragonal shape defects are observed within the MQW with 33% In composition by high resolution TEM. In addition, we found that V-defects result in different growth rates of the GaN barriers according to the degree of the bending of InGaN well layers, which changes the period thickness of the superlattice and might be the source of the multiple emission peaks observed in the In_xGa_1−xN/GaN MQWs with high in compositions.     

Optical study of InP quantum dots

Results of photoluminescence (PL) studies of self-organized nanoscale InP islands (quantum dots, QDs) in the In_0.49Ga_0.51P matrix, grown on a GaAs substrate by metalorganic vapor phase epitaxy (MOVPE), are presented. Dependences of the PL efficiency on temperature in the range 77–300 K and on excitation level at pumping power densities of 0.01–5 kW/cm² have been obtained. The PL spectra are a superposition of emission peaks from QDs and the wetting layer. Their intensity ratio depends on the pumping power and temperature, and the emission wavelength varies in the range 0.65–0.73 μm. At 77 K and low excitation level, InP QDs exhibit high temperature stability of the emission wavelength and high quantum efficiency. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 2, 2001, pp. 242–244. Original Russian Text Copyright ? 2001 by Vinokurov, Kapitonov, Nikolaev, Sokolova, Tarasov.     

Effects of growth interruption on the optical properties of AIGaAs/GaAs and GaAs/InGaAs quantum wells grown by atmospheric pressure organometallic chemical vapor deposition

In this study, the effects of growth interruptions on Al_0.17Ga_0.83As/GaAs and GaAs/ In_xGa_1-xAs quantum wells (QWs) grown by organometallic chemical vapor deposition (OMCVD) were assessed using low-temperature photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. Growth interruption times were varied between 60, 10, and 0 sec. For both material systems, as the interruption time was reduced, the ground-state QW transition energies increased, while the linewidths of the peaks decreased. For the Al_0.17Ga_0.83As/GaAs structures, 5 K PL data suggests that the incorporation of impurities is enhanced by longer growth interruption times. In addition, as the interruption time was reduced, the energy separation between the 5 K PL and PLE peaks (Stokes shift) decreased, and was as low as 2.6 meV for no interruption. For GaAs/In_0.11Ga_0.89As samples, 2 K PL data indicated that the incorporation of donor species was not a function of the growth interruption time.     

Growth and characterization of (111)B InGaAs/GaAs multi-quantum well PIN diode structures

High quality piezoelectric strained InGaAs/GaAs multi-quantum well structures on (111)B GaAs substrates have been grown by solid-source molecular beam epitaxy in a PIN configuration. 10K photoluminescence (PL) shows narrow peaks with widths as low as 3 meV for a 25-period structure while room temperature (RT) PL shows several higher order peaks, normally forbidden, indicating breaking of inversion symmetry by the piezoelectric field. Furthermore, both the 10K PL peak position and the form of the RT PL spectra depend on the number of quantum wells within the intrinsic region, suggesting that the electric-field distribution is altered thereby. Diodes fabricated from these structures had sharp avalanche breakdown voltages (V_bd) and leakage currents as low as 8 × 10⁻⁶ A/cm² at 0.95 V_bd, indicating quality as high as in (100) devices. On leave from: Department de Ingeniera Electronica, Universidad Politecnica de Madrid, Madrid, Spain.     

Polarization-resolved photoluminescence piezospectroscopy of GaAs/Al0.35Ga0.65As:Be quantum wells

The photoluminescence (PL) of GaAs/Al_0.35Ga_0.65As:Be quantum wells is studied at temperatures of 77 and 300 K under conditions of uniaxial compression along the [110] direction. There are two main lines in the PL spectra; at zero pressure and T = 77 K, the peaks appear at 1.517 and 1.532 eV. Comparison of the pressure dependences of the peak positions and the polarization of the PL measured experimentally with those calculated theoretically gives evidence that, at T ≥ 77 K, these bands originate from the recombination of free electrons with heavy and light holes in the GaAs valence band.     

Optical and morphological properties of InGaAs/AIGaAs self-assembled quantum dot nanostructures for 980 nm room temperature emission

This work deals with the study of optical and morphological properties of InGaAs/AlGaAs quantum dot （QD） structures grown by molecular beam epitaxy （MBE）. Photoluminescence （PL） emission energies, activation energies of PL quenching and QD sizes are studied as functions of the Al content in the AlyGal-yAs confining layers （CL）. We show that the PL emission energy of In（Ga）As/AlyGal-yAs QD structures increases with increasing y and that the sizes of InAs/AlyGal-yAs QDs decrease with increasing y. By the comparison of the experimental results with those of an effective-mass model developed to calculate the QD fundamental transition energies, we show that the blueshift of emission energy has to be ascribed not only to the increase in barrier discontinuities that confine the carriers into QDs but even to effects related to changes of the QD morphology dependent on CL composition. Moreover, we show that the Al content in the barriers determines also the activation energy of thermal quenching of PL, which depends on the thermal escape of carriers from QD levels. These studies resulted in the preparation of structures with efficient light-emission in the 980 nm spectral window of interest for lightwave communications.     

Investigation of microstructure and V-defect formation in In<Subscript>x</Subscript>Ga<Subscript>1−x</Subscript>N/GaN MQW grown using temperature-gradient metalorganic chemical vapor deposition

Temperature-gradient metalorganic chemical vapor deposition (MOCVD) was used to deposit In_xGa_1−xN/GaN multiple quantum well (MQW) structures with a concentration gradient of indium across the wafer. These MQW structures were deposited on low defect density (2×10⁸ cm⁻²) GaN template layers for investigation of microstructural properties and V-defect (pinhole) formation. Room temperature (RT) photoluminescence (PL) and photomodulated transmission (PT) were used for optical characterization, which show a systematic decrease in emission energy for a decrease in growth temperature. Triple-axis x-ray diffraction (XRD), scanning electron microscopy, and cross-sectional transmission electron microscopy were used to obtain microstructural properties of different regions across the wafer. Results show that there is a decrease in crystal quality and an increase in V-defect formation with increasing indium concentration. A direct correlation was found between V-defect density and growth temperature due to increased strain and indium segregation for increasing indium concentration.     

Effect of shroud flow on high quality InxGa1−xN deposition in a production scale multi-wafer-rotating-disc reactor

High quality InGaN thin films and InGaN/GaN double heterojunction (DH) structures have been epitaxially grown on c-sapphire substrates by MOCVD in a production scale multi-wafer-rotating-disc reactor between 770 to 840°C. We observed that shroud flow (majority carrier gas in the reaction chamber) is the key to obtaining high quality InGaN thin films. High purity H₂ as the shroud flow results in poor crystal quality and surface morphology but strong photolumines-cence (PL) at room temperature. However, pure N₂ as the shroud flow results in high crystal quality InGaN with an x-ray full width at half maximum (FWHM)_InGaN(0002) of 7.5 min and a strong room temperature PL peaking at 400 nm. In addition, InGaN/GaN single heterojunction (SH) and DH structures both have excellent surface morphology and sharp interfaces. The full width at half maximum of PL at 300K from an InGaN/GaN DH structure is about 100 meV which is the best reported to date. A high indium mole fraction in InGaN of 60% and high quality zinc doped InGaN depositions were also achieved.     

Gas-Source molecular beam epitaxy and characterization of inGaAs/lnGaAsP quantum well structures on InP

In this paper, we report the effect of using a group-V residual source evacuation (RSE) time on the interfaces of InGaAs/lnGaAsP quantum wells (QWs) grown by gas-source molecular beam epitaxy. High-resolution x-ray rocking curve and low-temperature photoluminescence (PL) were used to characterize the material quality. By optimizing the RSE time, a PL line width at 15K as narrow as 6.6 meV is observed from a 2 nm wide single QW, which is as good as or better than what has been reported for this material system. Very sharp and distinct satellite peaks as well as Pendellosung fringes are observed in the x-ray rocking curves of In_xGa_1−xAs/InxGa_1−xAS_yP_1−y multiple QWs, indicating good crystalline quality, lateral uniformity, and vertical periodicity. Theoretical considerations of the PL linewidths of In_xGa_1−xAs/InxGa_1−xAS_yP_1−y single QWs show that for QW structures grown with the optimized RSE time, the PL linewidth is mainly due to alloy scattering, whereas the contribution from interface roughness is small, indicating a good interface control.