LiF晶体的F_2、F_2~ 、F_2~-色心的形成及激光性能测定的研究

本文报导了LiF晶体中一种缺陷——色心的形成及色心激光性能测试的方法。对辐照损伤赋色的LiF晶体吸收谱和荧光光谱做了分析,并进行了激光振荡的实验。以LiF晶体中F_2,F_2~ 、F_2~-心为激光工作色心,已实现了F_2,F_2~ ,和 F_2~-色心脉冲可调谐激光输出。     

连续LiF:F_2~-色心激光器

一、引言 F_2~-色心从基态到第一激发态的吸收带有很高的辐照稳定性,并能在室温下产生近红外宽带振荡。在1978年Gusev实现了短时间工作的LiF:F_2~-心的连续振荡,1981年他和Ronoplin合作用环型谐振腔获得LiF:F_2~-连续输出,但由于未解决晶体的过热问题,不能长时间稳定工作。本实验较好地解决了晶体的过热问题,获得了F_2~-心的连续及准连续宽带振荡。 二、晶体的制备     

室温工作的高效率脉冲LiF色心(F_2~-)的激光输出

目前,工作在室温有实用意义的可实现近红外调谐激光运转的色心激光晶体,主要是LiF晶体中的F_2~-心和F_2~ 心。最近我们对于高效率F_2 心的宽光带脉冲激光输出的研究及其倍频的研究获得了新的进展,在实验室里已获得liF色心(F_2~-)的脉冲激光输出及转化为可见的黄光倍频效应。     

LiF晶体色心的形成和色心激光振荡的实验研究

本文从实验上研究了用γ射线辐照 LiF 晶体形成色心。用不同剂量形成的色心是不同的。选择10~7伦琴最佳剂量形成高密度的 F_2心,并对 F_2和F_2~ 心激光振荡特性进行了观测。对提高 F_2~ 心激光寿命作了讨论。     

LiF∶F_2~-晶体新型被动 Q 开关

一、引言用~(60)Co源γ射线辐照的LiF晶体,不仅是一种激光材料,而且也是一种良好的被动调Q元件。F_2~-心在室温下很稳定,长期放置不易褪色。随辐照剂量和原材料中杂质成分不同,一般F_2~-心寿命可达3～8年。LiF:F_L~-心晶体被动Q开关,与常用KDP和LiNbO_3等晶体主动开关相比,不需要复杂的供电电源,不存在KDP的潮解现象,插入损耗低,操作简单,导热性高,加工简便,抗损伤阈值高,毫微秒脉冲可达40GW/cm~2和成本低廉等。使用时只需放入谐振腔内即可。和五甲川染料相     

LiF晶体中F_2~+心的形成和激光振荡研究

本文报导以Y射线辐照纯LiF晶体获得色心,选择4×10Rad剂量辐照产生的高密度F_2心,用二步法光致电离使F_2心转化为高密度F_2~+心,这样获得的F_2~+心近红外脉冲激光输出较稳定。     

产生高密度室温稳定F_2~+色心的实验新方法以及有关机理的理论研究

采用新的低温装置,大剂量电子束辐照掺有(OH)~-的LiF晶体,产生了高密度室温稳定的F_2~+色心。这种F_2~+色心的激发谱峰值位置在608nm附近。相对于文献报道的普通LiF晶体F_2~+色心的吸收峰值(645nm)有较大的紫移。这种F_2~+色心的吸收带很宽,并具有良好的室温稳定性和抗光漂白特性。分析了室温辐照与低温辐照样品的不同特点,提出了低温大剂     

用于红宝石调Q的饱和吸收晶体

众所周知,用γ射线辐照的纯LiF晶体,会产生各种类型的色心——F,F_2,F_2~ 和F_2~-等。其中F_2、F_2~ 和F_2~-具有类似的四能级结构,并已产生可调谐的激光输出。     

高功率激励LiF:F_2晶体激光器振荡特性

在近红外光谱区,将脉冲固体激光辐射转变成可调谐辐射的效率大大提高的途经之一是采用新型的激活介质。尤其是,具有辐照色心的碱卤晶体乃是这种激活介质。这种介质具有广阔的实际应用前景与LiF:F_2~ 和LiF:F_2~-晶体室温下振荡辐射有关。这种介质激光器可以连续地复盖0.84～1.15μm(F_2~ )和1.08～1.26μm(F_2~-)光谱区。迄今为止,都是采用型工业用激光器作为色心晶体激光器的泵浦源。在此情况下LiF:F_2~-晶体激光器的振荡能量于非选择腔     

LiF晶体中色心的生成及其稳定性

众所周知,含有色心的碱卤晶体是实现可调谐激光的重要固体工作物质。LiF晶体则是这类材料中具有突出优点的一种。首先,LiF晶体中的色心在室温下有较高的荧光量子效率,故可在室温下实现激光振荡,这对很多实际应用无疑有着重要意义。其次,LiF晶体在空气中放置不易潮解,这就不必来用额外的防潮措施。第三,LiF晶体有高的热导率(0.103W/cm.℃)及高的破坏阈值(在1.06μm处为20GW/cm~2),这很适合用在高功率或高重复频率激光系统中。到目前为止,LiF晶体中的F_2、F_2~ 及F_2~-心均已获得可调谐激光振荡。     

Performance improvement in tensile-strained In/sub 0.5/Al/sub 0.5/As/In/sub x/Ga/sub 1-x/As/In/sub 0.5/Al/sub 0.5/As metamorphic HEMT

This paper proposes a In/sub 0.5/Al/sub 0.5/As/In/sub x/Ga/sub 1-x/As/In/sub 0.5/Al/sub 0.5/As (x=0.3-0.5-0.3) metamorphic high-electron mobility transistor with tensile-strained channel. The tensile-strained channel structure exhibits significant improvements in dc and RF characteristics, including extrinsic transconductance, current driving capability, thermal stability, unity-gain cutoff frequency, maximum oscillation frequency, output power, power gain, and power added efficiency.     

Very low-noise Al/sub 0.3/Ga/sub 0.7/As/Ga/sub 0.65/In/sub 0.35/As/GaAs single quantum-well pseudomorphic HEMTs

AlGaAs/GaInAs/GaAs pseudomorphic HEMTs with an InAs mole fraction as high as 35% in the channel has been successfully fabricated. The device exhibits a maximum extrinsic transconductance of 700 mS/mm. At 18 GHz, a minimum noise figure of 0.55 dB with 15.0 dB associated gain was measured. At 60 GHz, a minimum noise figure as low as 1.6 dB with 7.6 dB associated gain was also obtained. This is the best noise performance yet reported for GaAs-based HEMTs.<>     

A 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode array

We report a 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode (APD) array. The mean breakdown voltage of the APD was 57.9 V and the standard deviation was less than 0.1 V. The mean dark current was /spl sim/2 and /spl sim/300 nA, and the standard deviation was /spl sim/0.19 and /spl sim/60 nA at unity gain (V/sub bias/ = 13.5 V) and at 90% of the breakdown voltage, respectively. External quantum efficiency was above 40% in the wavelength range from 1.0 to 1.6 /spl mu/m. It was /spl sim/57% and /spl sim/45% at 1.3 and 1.55 /spl mu/m, respectively. A bandwidth of 13 GHz was achieved at low gain.     

Morphological and electrical characterization of SixCryCzBv thin films

Si_xCr_yC_zB_v thin films with several compositions have been studied for integration of high precision resistors in 0.8 μm BICMOS technology. These resistors, integrated in the back-end of line, have the advantage to provide high level of integration and attractive electrical behavior in temperature, for analog devices. The film morphology and the structure have been investigated through transmission electron microscopy analysis and have been then related to the electrical properties on the base of the percolation theory. According to this theory, and in agreement with experimental results, negative thermal coefficient of resistance (TCR) has been obtained for samples with low Cr content, corresponding to a crystalline volume fraction below the percolation threshold.Samples with higher Cr content exhibit, instead, a variation of the TCR as a function of film thickness: negative TCR values are obtained for thickness lower than 5 nm, corresponding to a crystalline volume fraction below the percolation threshold; positive TCR are obtained for larger thickness, indicating the establishment of a continuous conductive path between the Cr rich grains. This property seems to be determinant in order to assure the possibility to obtain thin film resistors almost independent on the temperature.     

Al/sub 0.3/Ga/sub 0.7/As/In/sub x/Ga/sub 1-x/As (0/spl les/x/spl les/0.25) doped-channel field-effect transistors (DCFET's)

The properties of both lattice-matched and strained doped-channel field-effect transistors (DCFET's) have been investigated in AlGaAs/In/sub x/Ga/sub 1-x/As (0/spl les/x/spl les/0.25) heterostructures with various indium mole fractions. Through electrical characterization of grown layers in conjunction with the dc and microwave device characteristics, we observed that the introduction of a 150-/spl Aring/ thick strained In/sub 0.15/Ga/sub 0.85/As channel can enhance device performance, compared to the lattice-matched one. However, a degradation of device performance was observed for larger indium mole fractions, up to x=0.25, which is associated with strain relaxation in this highly strained channel. DCFET's also preserved a more reliable performance after biased-stress testings.<>     

Highly linear Al/sub 0.3/Ga/sub 0.7/N-Al/sub 0.05/Ga/sub 0.95/N-GaN composite-channel HEMTs

We report an Al/sub 0.3/Ga/sub 0.7/N-Al/sub 0.05/Ga/sub 0.95/N-GaN composite-channel HEMT with enhanced linearity. By engineering the channel region, i.e., inserting a 6-nm-thick AlGaN layer with 5% Al composition in the channel region, a composite-channel HEMT was demonstrated. Transconductance and cutoff frequencies of a 1 /spl times/100 /spl mu/m HEMT are kept near their peak values throughout the low- and high-current operating levels, a desirable feature for linear power amplifiers. The composite-channel HEMT exhibits a peak transconductance of 150 mS/mm, a peak current gain cutoff frequency (f/sub T/) of 12 GHz and a peak power gain cutoff frequency (f/sub max/) of 30 GHz. For devices grown on sapphire substrate, maximum power density of 3.38 W/mm, power-added efficiency of 45% are obtained at 2 GHz. The output third-order intercept point (OIP3) is 33.2 dBm from two-tone measurement at 2 GHz.     

Comparison between Pt/TiO2/Pt and Pt/TaOX/TaOY/Pt based bipolar resistive switching devices

Nonvolatile memories have emerged in recent years and have become a leading candidate towards replacing dynamic and static random-access memory devices. In this article, the performances of TiO₂ and TaO₂ nonvolatile memristive devices were compared and the factors that make TaO₂ memristive devices better than TiO₂ memristive devices were studied. TaO₂ memristive devices have shown better endurance performances (10⁸ times more switching cycles) and faster switching speed (5 times) than TiO₂ memristive devices. Electroforming of TaO₂ memristive devices requires~4.5 times less energy than TiO₂ memristive devices of a similar size. The retention period of TaO₂ memristive devices is expected to exceed 10 years with sufficient experimental evidence. In addition to comparing device performances, this article also explains the differences in physical device structure, switching mechanism, and resistance switching performances of TiO₂ and TaO₂ memristive devices. This article summarizes the reasons that give TaO₂ memristive devices the advantage over TiO₂ memristive devices, in terms of electroformation, switching speed, and endurance.     

Broadband microwave noise characteristics of high-linearity composite-channel Al/sub 0.3/Ga/sub 0.7/N/Al/sub 0.05/Ga/sub 0.95/N/GaN HEMTs

We report broadband microwave noise characteristics of a high-linearity composite-channel HEMT (CC-HEMT). Owing to the novel composite-channel design, the CC-HEMT exhibits high gain and high linearity such as an output third-order intercept point (OIP3) of 33.2 dBm at 2 GHz. The CC-HEMT also exhibits excellent microwave noise performance. For 1-/spl mu/m gate-length devices, a minimum noise figure (NF/sub min/) of 0.7 dB and an associated gain (G/sub a/) of 19 dB were observed at 1 GHz, and an (NF/sub mi/) of 3.3 dB and a G/sub a/ of 10.8 dB were observed at 10 GHz. The dependence of the noise characteristics on the physical design parameters, such as the gate-source and gate-drain spacing, is also presented.