Blue lasing at room temperature in an optically pumped lattice-matched AlInN=GaN VCSEL structure

Laser action with low threshold average pump power density (~50 W - cm^-2 ) at room temperature is reported for a crack-free planar vertical cavity surface emitting laser (VCSEL) structure based on a bottom lattice-matched AllnN/GaN distributed Bragg reflector (DBR) and a top dielectric DBR. The cavity region, formed by n- and p-type GaN layers surrounding only three InGaN/GaN quantum wells, corresponds to a typical active region suitable for an electrically driven VCSEL. In addition to low threshold, a spontaneous emission coupling factor beta ~ 2 x 10^-10 is derived for this ready-to-be-processed laser structure.     

Small-frequency-difference stabilization of laser diodes using12C2H2 and 13C2H2 absorption lines for transmitter and local oscillator ofoptical heterodyne systems

Small-frequency-difference stabilization of distributed Bragg reflector (DBR) laser diodes has been demonstrated for the first time by using vibrational-rotational absorption of ¹²C₂H ₂ and ¹³C₂H₂ molecules. Frequency stabilization of two DBR laser diodes has been carried out at a wavelength of about 1.536 μm. The frequency difference between the two stabilized lasers was evaluated to be 9 GHz by the beat spectrum measurement. The experimental results suggest that such a pair of frequency-stabilized laser diodes with a small frequency difference could be used as the transmitter and local oscillator of optical heterodyne systems     

Demonstration of GaN MIS diodes by using AlN and Ga2O3(Gd2O3) as dielectrics

GaN MIS diodes were demonstrated utilizing AlN and Ga₂O₃(Gd₂O₃) as insulators. A 345 Å of AlN was grown on the MOCVD grown n-GaN in a MOMBE system using trimethylamine alane as Al precursor and nitrogen generated from a SVT RF N₂ plasma. For the Ga₂O₃(Gd₂O₃) growth, a multi-MBE chamber was used and a 195 Å oxide was E-beam evaporated from a single crystal source of Ga₅Gd₃O₁₂. The forward breakdown voltage of AlN and Ga₂O₃(Gd₂O₃) diodes are 5 and 6 V, respectively, which are significantly improved over 1.2 V from that of a Schottky contact. From the C–V measurements, both kinds of diodes showed good charge modulation from accumulation to depletion at different frequencies. The insulator/GaN interface roughness and the thickness of the insulator were measured with X-ray reflectivity.     

Phase conjugation of CO2 laser radiation in a mediumwith thermal nonlinearity

An investigation of reflectivity and quality of phase conjugation of CO₂ laser radiation by four-wave mixing in a medium with thermal nonlinearity is discussed. High reflectivity produced by four-wave mixing in CCl₄ was demonstrated both for pulsed radiation (180%) and for CW radiation (20%). A self-pumped phase-conjugate mirror based on four-wave mixing with feedback was realized. Energy, spatial, spectral, temporal, and polarization characteristics of radiation generated by four-wave mixing with feedback in CCl₄ were investigated. The minimum threshold energy of the input signal was ≃8 mJ; the maximum energy reflectivity was about 5. The spatial structure of radiation generated in the scheme of four-wave mixing with feedback was investigated theoretically, and the conditions for phase conjugation, both for regular and for speckled signal beams, were determined     

用633nm的激光器监控峰值波长为 530nm的AlGaN/GaN DBR的生长

本文从理论和实验上研究了用633nm激光器干涉仪监控峰值反射波长为530nm的1/4光学厚度的AlGaN/GaN 分布布拉格反射器（DBR）的生长。首先采用传输矩阵法从理论上研究了不同周期厚度的AlGaN/GaN DBR的实时反射率随DBR生长厚度的变化。接着采用金属有机化合物气相外延法生长了两个与模拟结构相同的DBR样品。仿真结果和实验结果表明能够从DBR实时反射率随生长厚度变化的曲线形状判断DBR的结构参数。最后通过激光干涉仪实时监控生长了DBR发光二极管,光致发光实验证明DBR对发光二极管出射光的加强作用在期望波长范围内。     

GaN-Based High-Q Vertical-Cavity Light-Emitting Diodes

We report a fabrication and demonstration of a GaN-based high-Q vertical-cavity light-emitting diode (VCLED). The GaN VCLED is composed of a 25-pair high-reflectivity (98%) GaN/AlN distributed Bragg reflector (DBR), an eight-pair SiO₂/Ta₂O₅ dielectric DBR (99%), and a three-lambda optical thickness InGaN/GaN active region. It shows a very narrow linewidth of 0.52 nm, corresponding to a cavity Q -value of 895 at a driving current of 10 mA and a dominant emission peak wavelength at 465.3 nm. In addition, this VCLED emission linewidth continues to decrease with an increasing injection current, suggesting a possible realization of GaN-based vertical-cavity surface emitting lasers.     

材料结构对AlGaN基分布布拉格反射镜特性的影响

采用低压MOCVD技术生长了AlGaN／GaN、AlGaN／AlN等多种交替生长结构的半导体多层膜分布布拉格反射镜（DBR）。利用X射线衍射、扫描电子显微镜（SEM）、原子力显微镜（AFM）等测量手段对材料的物理特性进行了分析表征。结果表明，材料结构对DBR的性能影响很大。通过材料的优化生长，获得了反射率高达93.5％、中心波长和发射率都接近理论值的AlGaN／AlNDBR材料。     

In situ growth monitoring of AlGaN/GaN distributed Bragg reflectors at 530 nm using a 633 nm laser

The metal-organic chemical vapor deposition(MOCVD) growth of AlGaN/GaN distributed Bragg reflectors (DBR) with a reflection peak at 530 nm was in situ monitored using 633 nm laser reflectometry.Evolutions of in situ reflected reflectivity for different kinds of AlGaN/GaN DBR were simulated by the classical transfer matrix method.Two DBR samples,which have the same parameters as the simulated structures,were grown by MOCVD.The simulated and experimental results show that it is possible to evaluate the DBR...     

Lasing Behavior of BMPPV:PVK Mixture in Microcavity

The surface emitting microcavity is formed by sandwiching a polymer film containing poly (para-phenylene vinylene) (BMPPV) and poly (N-vinylcarbazole)(PVK) between a DBR with a reflectivity of 99.5% and a silver film.The sample is optically pumped by a 337.1 nm line of nitrogen laser with 10 ns pulses at 20 Hz repetition rate.The lasing phenomenon is observed in BMPPV and PVK mixture microcavity .The full width at half maximum( FWHM) is 6 nm at the peak wavelength of 460 nm.The lasing threshold energy is estimated to be about 5μJ.     

High quantum efficiency and narrow absorption bandwidth of thewafer-fused resonant In0.53Ga0.47As photodetectors

We demonstrate greater than 90% quantum efficiency in an In_0.53Ga_0.47As photodetector with a thin (900 Å) absorbing layer. This was achieved by inserting the In_0.53 Ga_0.47As/InP epitaxial layer into a microcavity composed of a GaAs/AlAs quarter-wavelength stack (QWS) and a Si/SiO₂ dielectric mirror. The 900-Å-thick In_0.53 Ga_0.47As layer was wafer fused to a GaAs/AlAs mirror, having nearly 100% power reflectivity. A Si/SiO₂ dielectric mirror was subsequently deposited onto the wafer-fused photodiode to form an asymmetric Fabry-Perot cavity. The external quantum efficiency and absorption bandwidth for the wafer-fused RCE photodiodes were measured to be 94±3% and 14 nm, respectively. To our knowledge, these wafer-fused RCE photodetectors have the highest external quantum efficiency and narrowest absorption bandwidth ever reported on the long-wavelength resonant-cavity-enhanced photodetectors     

AlGaInP microcavity light-emitting diodes at 650 nm on Gesubstrates

We demonstrate microcavity light emitting diodes (MCLEDs) emitting at 650 nm on Ge substrates. Ge has the advantage of lower cost and higher strength compared to GaAs substrates. The multi-quantum well microcavity devices consisted of AlGaAs-based distributed Bragg reflector (DBR) mirrors, AlGaInP active material with an additional 5-μm p-Al_0.55Ga_0.45As current spreading layer on top of the p-DBR. A maximum external quantum efficiency of 4.35% and an optical power higher than 5 mW was obtained for a device with 200-μm diameter. The results indicate the potential use of MCLEDs on Ge for visible LEDs     

Room temperature pulsed operation of 1.5 μm GaInAsP/InPvertical-cavity surface-emitting laser

Room-temperature pulsed operation of a GaInAsP/InP vertical-cavity surface-emitting laser diode (VCSELD) with an emission wavelength near 1.55 μm is reported. A double heterostructure with a 34-pair GaInAsP (λ_g=1.4 μm)/InP distributed Bragg reflector (DBR) was grown by metalorganic chemical vapor deposition (MOCVD). The measured reflectivity of the semiconductor DBR is over 97% and threshold current is 260 mA for a 40-μmφ device with a 0.88-μm-thick active layer. Threshold current density is as low as 21 kA/cm² at room temperature     

AlGaN /GaN分布布拉格反射镜的设计与表征

设计了反射中心波长为500nm的Al0.3Ga0.7N/GaN和AlN/GaN两种分布布拉格反射镜（DBR）,并采用光学传递矩阵方法对其光谱反射率进行了理论上的模拟.采用金属有机物化学气相淀积（MOCVD）技术在蓝宝石衬底上制备了样品.实际测量的样品反射谱中有明显的反射峰,但峰值波长与理论设计有偏差,峰值反射率也比理论设计值偏低.SEM和AFM测量结果表明：这是由生长层厚与设计的偏差和界面不平整引起的.     

Transport properties of AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors with Al2O3 of different thickness

The Al₂O₃ as a gate oxide and passivation was used to study the transport properties of AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors (MOSHFETs). Performance of the devices with Al₂O₃ of different thickness between 4 and 14 nm prepared by metal–organic chemical vapor deposition (MOCVD) and with 4 nm thick Al₂O₃ prepared by Al sputtering and oxidation was investigated. All MOS-devices yielded higher transconductance than their HFET counterparts, i.e. the transconductance/capacitance expected proportionality assuming the same carrier velocity was not fulfilled. A different electric field near/below the gate contact due to a reduction of traps is responsible for the carrier velocity enhancement in the channel of the MOSHFET. The trap reduction depends on the oxide used, as follows from the capacitance vs frequency dispersion for devices investigated. It is qualitatively in a good agreement with the different velocity enhancement evaluated, and devices with thinner oxide show higher traps reduction as well as higher transconductance enhancement. It is also shown that obtained conclusions can be applied well on performance of SiO₂/AlGaN/GaN MOSHFETs.     

Thermo-optical switching in Si/Si1-xGexdistributed Bragg reflectors

The authors report thermo-optical switching in a 92 layer Si/Si _0.7Ge_0.3 distributed Bragg reflector (DBR) grown by molecular beam epitaxy. Depending on the layer periodicity, this structure exhibited a positive or negative reflectivity switching λ=1.06 μm, with a switch-on time of less than 20 ns and reflectivity contrast ratios greater than 50%     

高反射性电流阻挡层用于提高InGaN/GaN发光二极管的光输出功率

由SiO₂/TiO₂分布布拉格反射镜(DBR)和Al镜组成的混合式反射电流阻挡层用于提高InGaN/GaN发光二极管的光输出功率。混合式反射电流阻挡层不仅增强了电流扩展效应而且有效的将射向p金属电极的光子反射防止其对p电极焊点附近光子的吸收。实验结果表明,淀积在p-GaN上1.5个周期的SiO₂/TiO₂DBR和Al镜在455nm垂直入射时的反射率高达97.8%。在20mA的工作电流下,与没有电流阻挡层的发光二极管相比,生长1.5对SiO₂/TiO₂ DBR和Al镜作为电流阻挡层的发光二极管的光输出功率提高了12.5%,且光输出功率的分布更加均匀。     

Spontaneous emission factor of a microcavity DBR surface-emittinglaser

The spontaneous emission factor (SEF) of a microcavity distributed Bragg reflector (DBR) surface-emitting laser has been obtained theoretically to investigate the possibility of the thresholdless lasing operation. Formulas expressing the spontaneous emission in a three-dimensional microcavity were obtained. By introducing the distribution of mode density in wavevector space, it is shown that the radiation pattern of spontaneous emission is deeply modified by the microcavity and is different from that in free space. Based on this result, the SEF and the emission lifetime are calculated as a function of emission spectral width and the size of the active region. It is found that the SEF exceeds 0.1, even though the spectral width is as large as 30 nm when the transverse size is smaller than 0.5 μm and the DBR reflectivity is larger than 90%     

Further investigations of a 2-μm Tm:YVO4 laser

The performance of a Tm:YVO₄ laser has been optimized by varying the thickness of the laser crystal and the reflectivity of the output coupler. This has led to the measurement of a slope efficiency of 48% for the laser output. Formulas describing the saturation of the pump and the upper laser level in the presence of up-conversion loss have been developed. Fitting of the experimental data to the saturation curves calculated using these formulas has yielded an up-conversion rate constant from ³F₄ to ³ H₅ of 2·10^-18 cm³ s^-1      

一种微腔有机发光二极管的设计与性能研究

设计了PPV为发光层、Ag和DBR为上下反射镜、结构为Glass/DBR/ITO/PPV/Ag的微腔有机发光二极管。应用特征矩阵法,系统地研究了DBR和银镜的性质对器件性能的影响。结果表明:1)当金属厚度较小时,随着厚度的增加,器件的反射峰值不断增加并且蓝移,但是当厚度达到100 nm后,再增加厚度反射谱基本上没变化;2)随着DBR周期数的增加,器件的反射谱峰值不断增大,峰值半宽度不断变窄。3)器件的EL谱的峰值随着金属反射率的增加不断增大,而随着DBR反射率的增加是先增加后减小的。并给出了不同条件下DBR的最优化选择依据。     

A Low Phase-Noise X-Band MMIC VCO Using High-Linearity and Low-Noise Composite-Channel Al0.3Ga0.7N/Al0.05Ga0.95N/GaN HEMTs

A low phase-noise X-band monolithic-microwave integrated-circuit voltage-controlled oscillator (VCO) based on a novel high-linearity and low-noise composite-channel Al_0.3Ga_0.7N/Al_0.05Ga_0.95 N/GaN high electron mobility transistor (HEMT) is presented. The HEMT has a 1 mumtimes100 mum gate. A planar inter-digitated metal-semiconductor-metal varactor is used to tune the VCO's frequency. The polyimide dielectric layer is inserted between a metal and GaN buffer to improve the Q factor of spiral inductors. The VCO exhibits a frequency tuning range from 9.11 to 9.55 GHz with the varactor's voltage from 4 to 6 V, an average output power of 3.3 dBm, and an average efficiency of 7% at a gate bias of -3 V and a drain bias of 5 V. The measured phase noise is -82 dBc/Hz and -110 dBc/Hz at offsets of 100 kHz and 1 MHz at a varactor's voltage (V_tune)=5 V. The phase noise is the lowest reported thus far in VCOs made of GaN-based HEMTs. In addition, the VCO also exhibits the minimum second harmonic suppression of 47 dBc. The chip size is 1.2times1.05 mm²