Frequency-Tunable Terahertz-Wave Generation from GaP Using Cr:Forsterite Lasers

We have constructed THz spectrometers using the widely frequency-tunable THz-wave generated from GaP crystal pumped at 1.2 µm region using two Cr:forsterite lasers and compared with that pumped at 1 µm region using a YAG laser and an optical parametric oscillator (OPO). The systems have sufficient resolution for observation of solids and liquids at room temperature. We have measured Terahertz absorption spectra of all 20 kinds of amino acids which form proteins.     

Luminescence decay kinetics in GaP:Bi and GaP:N

The lifetime of excitons bound to isoelectronic traps in GaP is studied as a function of temperature, excitation energy and intensity. The photoluminescence was excited both selectively and above the gap by using a pulsed, tunable dye laser with photon flux varying in the range of 10¹⁴–10¹⁹ photons/cm² per pulse. GaP:Bi shows a strong intensity dependence of τ(T) in the temperature range of 40–60 K due to the thermal activation of the electron. Similarly, GaP:N shows this behavior in the range of 20–100 K. In this case, two activation processes can be identified: release of the bound exciton into the free exciton band and dissociation of the exciton. The observed dependence of τ(T) on both excitation energy and intensity indicate that saturable deep traps (shunt paths) deplete the excess free carriers. These traps can be completely saturated in GaP:N while only partial saturation is achieved in GaP:Bi. The kinetic equations are written for GaP:Bi and solved numerically assuming quasiequilibrium conditions. Fitting this model to the experimental results yields the capture cross sections for carriers by Bi and by the deep traps as well as the concentration of the latter.     

离子注入中污染的产生及防护

本文概述了离子注入过程中污染产生的原因和防止污染的措施，特别强调了对微粒污染和金属污染的防护以满足ＵＬＳＩ加工对离子注入的要求。     

Degradation of GaP:N LEDs

The degradation of light output with operating time has been studied for nitrogen doped GaP light emitting diodes fabricated from vapor phase epitaxial material. The degradation is found to saturate at a non-zero value of efficiency. The process is characterized in terms of a degradation rate constant and the saturation value of efficiency. The rate is found to be a strong function of current density during operation and to a lesser degree materials parameters such as dislocation density. The saturation value appears to be independent of these parameters. The degradation is specifically associated with a decrease in the minority carrier lifetime in the p-side of these diffused LEDs. A model for the generation of non-radiative recombination centers which describes the degradation process quantitatively is presented.     

DETERMINATION OF GENERATION LIFETIME FROM C-t TRANSIENTS UNDER LINEAR VOLTAGE RAMP BIAS

When a linear voltage ramp is applied to the gate of a MOS capacitor,a capacitance-time(C-t)transient is observed.The MOS capacitor is biased into strong inversion before apply-ing the voltage ramp in order to eliminate surface generation.From C-t transient curve obtainedexperimentally the minority carrier generation lifetime in semiconductor can be determined.Theexperimental results show that for the same sample the lifetimes extracted from C-t curves un-der varying voltage sweep rates are close each other,and they are consistent with the lifetimesextracted by saturation capacitance method.     

Hemispherical GaP:N green electroluminescent diodes

Hemispherically shaped, reduced active junction area, GaP green light-emitting diodes have been fabricated by mechanical polishing and electrochemical etching from $\text{p-n}$ junctions grown by double liquid phase epitaxy on pulled crystal substrates. The hemispherical structure with the light-emitting area restricted to the central portion of the flat surface represents an idealized geometry in which to study luminescent generation and optical coupling phenomena in green-emitting material and devices. Experiments reported here show that the efficiency with which internally generated light is extracted from these GaP structures is at least twice as large as in encapsulated reduced junction area slurry cut cubical dice or mesa diodes. The junction reduction procedure is described and the properties of reduced junction area cubical diodes examined. A maximum external quantum efficiency of 0·41 per cent has been achieved with the hemispherical structure from a crystal which for other geometric devices yielded a maximum external efficiency of 0·17 per cent.     

The causes of emitting-power instability in GaP:N LED

A complex study of injection-enhanced processes in GaP:N light emitting diodes under forward bias (I = 5–30 mA) during the first 2–5 min has been carried out. The electrical, electroluminescent methods, DLTS technique and the method of secondary emission mass spectroscopy have been used. It has been shown that the instability of luminous power of GaP:N LEDs is associated with recombination-enhanced annealing defects in the active region of devices, rather than processes at the contacts. It has been found, that stable LEDs have a significantly higher concentration of O, C and their compounds.A reliable physical model of the processes involved is proposed.     

Degradation induced formation of extended defects in GaP:N LED's

The light output degradation of commercial VPE GaP:N LED's was studied by monitoring minority carrier lifetime and deep level spectra. It was found that the decrease of the quantum efficiency can be completely accounted for by the formation of a nonradiative recombination center T6. T6is identified as a vacancy cluster, a model suggested by the formation-annihilation properties of this deep level.     

Optical amplification characteristics of Cr:LiSAF and Cr:LiCAFunder flashlamp-pumping

Small-signal gain measurements of flashlamp-pumped Cr-doped LiSAF and LiCAF are summarized for a range of material parameters. Flashlamp pumping allows efficient energy storage for both materials in the order 1.6 to 2.6% of the electrical pump energy. Small-signal gain values of up to 0.16 cm^-1 are measured for Cr:LiSAF and 0.09 cm^-1 for Cr:LiCAF. The gain of both materials is found to be affected by excited state absorption and upconversion. In addition the implications of these results for the design of laser/amplifier systems are discussed     

用微区光学方法研究GaP:ZnO红光外延片

用微区光致发光和拉曼散射光谱比较了国内外Gap:ZnO红光二极管产品的结构,在国内首先实现了用微区光学方法检测LED外延片并进行生产工艺的改进,对典型样品进行了微区光致发光的测试,比较外延片横截面上不同厚度层的光致发光,非常明显地看出主要发光区是在P区。通过合理扩展P层发光区的厚度相应地增加了光致发光的总光强,提高了产品的生产成品率。     

Comparison of CW THz Wave Spectrometer with Laser Diode Excitation and Pulsed THz Wave Spectrometer with Cr:forsterite Sources Based on Difference Frequency Generation of Near-infrared Lasers in GaP

We constructed two types of terahertz (THz) spectrometers with automatic scanning control based on the difference frequency generation method by the excitation of the phonon-polariton mode in GaP. The pulsed THz wave spectroscopic systems were based on an optical parametric oscillator and Nd: YAG laser sources having a frequency resolution of 1.5 GHz, and on Cr:fosterite sources with a resolution of 20 GHz. Following these, we recently constructed a continuous wave (CW) THz wave spectroscopic system with laser diode excitation. One of the advantages of the CW THz wave spectrometer is its wide frequency tuning range with fine frequency resolution of < 8 MHz. In this study, we compare both types of spectrometers (pulsed versus CW) to show the characteristics of each system in terms of frequency resolution. The absorption spectra of a non-deformed white polyethylene crystal and ultra-high molecular weight polyethylene with/without deformation are measured by using the CW THz wave spectrometer and pulsed THz wave spectrometer. The effect of the high-resolution CW THz wave spectrometer is shown based on the THz spectroscopic results.     

闪光灯泵浦的Cr:LiSAF激光器

报道了闪光灯泵浦的国产ＣｒＬｉＳＡＦ棒激光器的脉冲运转特性,实验得到的最大输出能量为９９２ｍＪ,斜率效率为１．５％。     

Cr:LiSAF slab laser performance

The performance of a flash-lamp pumped Cr³⁺: LiSrAlF ₆ multi-bounce slab laser is reported. The slab was conductively-cooled by a sapphire window which also transmitted the pump light. Laser output of 9 mJ and a slope efficiency of 0.061% were obtained although less than 15% of the total pump aperture was used     

Multi-terawatt femtosecond Cr:LiSAF laser

We discuss the design of a Cr:LiSAF laser system capable of generating ultrashort, 90-fs Fourier-transform limited pulses with a peak power of 8 TW. Using chirped pulse amplification and flashlamp-pumped Cr:LiSAF amplifiers this system incorporates a regenerative amplifier and three additional double-pass amplifiers with increasing aperture up to 25 mm. The temporal performance as well as the spatial beam quality are discussed in detail. We discuss extension of this system to the Petawatt power level     

闪光灯泵浦Cr：LiCAF激光器的实验研究

实现了闪光灯泵浦Ｃｒ：ＬｉＣＡＦ激光器的脉冲运转．在最佳耦合输出条件下获得斜率效率为２．２０％、转换效率为１．３６％的激光输出。研究结果表明．对于闪光灯泵浦的Ｃｒ：ＬＩＣＡＦ激光器．较高的掺杂浓度有利于降低激光阈值并提高输出能量和效率。实验中观察到激光脉冲尖峰振荡中的类自调Ｑ现象。     

Cr2+:ZnSe中红外激光器

Cr2 掺杂Ⅱ-Ⅵ族化合物在中红外波段的输出,在气体检测、遥感、通信、眼科医学、神经外科等领域有着重要的应用前景.目前已经获得了最大1.7 W的连续输出功率,18.5 W的平均脉冲功率,1100 nm的调谐范围和最窄4 ps的脉宽.对Cr2 :ZnSe连续、脉冲、随机纳米激光器以及其它的Cr2 掺杂Ⅱ-Ⅵ族化合物激光器的最新的国内外研究进展进行了综述.     

Performance of a Cr:YAG laser

We report on the performance of a Cr⁴⁺:YAG laser, tunable over the range from 1.32 to 1.53 μm, under different operating conditions. Laser action has been achieved by pumping with a Nd:YAG laser in the Q-switched mode and cw mode and with a Cr:Nd:GSGG laser in the long pulse mode. Slope efficiencies up to 22% in the Q-switched mode have been achieved. The lowest threshold was 30 mJ for the long pulse pumped mode. Excited state absorption seems to limit the tuning range and the output characteristics     

A comparison of gamma-induced degradation and forward bias-induced degradation in GaP:Zn,0 LEDs

Both the effects of gamma irradiation and high-current forward bias on GaP:Zn,0 light emitting diodes (LEDs) have been studied by measuring constant current 76K electroluminescence (EL) spectra below 1000 nm, total light output at room temperature, and capacitance transients using the technique of deep level transient spectroscopy (DLTS). The LEDs were divided into two sets; a control set which was subjected only to forward bias, and a set exposed to gamma irradiation and forward bias. The results indicate that gamma-induced light output degradation occurs through a different mechanism than forward bias-induced degradation of the control LEDs. Gamma irradiation, which has no effect on the Zn-O concentration, degrades the light output through the introduction of competing non-radiative recombination centers which reduce the minority carrier lifetime. In contrast, forward bias-induced light output degradation is primarily due to a reduction in Zn-O concentration through the apparent recombination-enhanced interaction of Zn-O centers with impurities rather than defects. This work was supported in part by the Air Force Weapons Laboratory (AFWL) Kirtland AFB, Albuquerque, NM under P. O. 77-027, and in part by the U. S. Department of Energy (DOE) under contract number AT(29-1)789.     

闪光灯泵浦Cr：LiSAF可调谐激光器

报道闪光灯泵浦掺铬氟化铝锶锂（Ｃｒ：ＬｉＳＡＦ可调谐激光的实验结果。调谐范围为７８６～９３４ｎｍ，最大输出能量为４２０ｍＪ，斜率效率为１．２６％。对实验结果进行了讨论。