Improved gain performance of high concentration Er/sup 3+/-Yb/sup 3+/-codoped phosphate fiber amplifier

The rate equations and power evolution equations of erbium/ytterbium codoped phosphate fiber amplifiers are solved numerically and its results are compared with measured data in literature. Based on the numerical analysis, optimal erbium and ytterbium codoping concentrations are supposed, and with a pump power of 224 mW and a fiber length of 3.6 cm, the internal gain of 31.0 dB and gain per unit length of 8.6 dB/cm may be achieved in the fiber with the optimal codoping concentrations.     

Negative charge induced degradation of PMOSFETs with BF/sub 2/-implanted p/sup +/-poly gate

A new degradation phenomenon on thin gate oxide PMOSFETs with BF/sub 2/ implanted p/sup +/-poly gate has been demonstrated and investigated. The cause of this type of degradation is a combination of the boron penetration through the gate oxide and charge trap generation due to the presence of fluorine in the gate oxide and some other processing-induced effects. The negative charge-induced degradation other than enhanced boron diffusion is studied in detail here. The impact of this process-sensitive p/sup +/-poly gate structure on deep submicron CMOS process integration has been discussed.<>     

High repetition rate passively Q-switched Nd/sup 3+/:Cr/sup 4+/ all-fibre laser

A passively Q-switched fibre laser comprising an Nd/sup 3+/-doped gain fibre spliced to a new Cr/sup 4+/-doped saturable absorber fibre delivers 0.3 nm-bandwidth continuous pulsed laser beam at 1084 nm, with 38 to 84 kHz repetition rate, and 3.0 to 6.4 /spl mu/s pulse duration.     

All-epitaxial current- and mode-confined AlGaAs/GaAs VCSEL

An all-epitaxial current- and mode-confining vertical-cavity surface-emitting laser is demonstrated that eliminates the need for any post-growth oxidation step. The current and optical mode are self-aligned and confined to the same lithographically defined area in an AlGaAs cavity.     

Laser diode pumped Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped fluoride fiber amplifiers operating at 1.3 mu m

Both Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped singlemode fibres with high numerical apertures are pumped by laser diodes with InGaAs/GaAs strained quantum well structures. A net gain of 5.2 dB is obtained from Pr/sup 3+/-doped fluoride fibre pumped by laser diodes operating at 1.1017 mu m and a net gain of 3.2 dB is obtained from Pr/sup 3+/-Yb/sup 3+/-codoped fibre pumped by laser diodes operating at 0.98 mu m. The pumping efficiency difference between Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped fibre is discussed.<>     

Modeling and optimization of short Er/sup 3+/-Yb/sup 3+/ codoped fiber lasers

A theoretical study of short Er/sup 3+/- Yb/sup 3+/ codoped fiber lasers (EYDFLs) is presented. Examples include centimeter-length EYDFLs pumped at 978 nm, with distributed Bragg reflector (DBR) mirrors at both fiber ends. Approximate quasi-analytical solutions are shown to be in excellent agreement with the exact numerical solution of the rate equations. Using the quasi-analytical model, we demonstrate a design optimization of a short EYDFL. The effects of the Yb/sup 3+/ concentration, laser wavelength, output mirror reflectivity, and pump wavelength are considered and discussed with relation to the optimal laser length and output efficiency.     

Femtosecond Cr/sup 4+/:YAG laser with 4 GHz pulse repetition rate

The construction of a compact, high-repetition-rate femtosecond Cr/sup 4+/:YAG laser is reported. Transform-limited pulses as short as 80 fs were generated at pulse repetition frequencies up to 4 GHz. The femtosecond pulses were tunable from centre wavelengths of 1505 to 1550 nm.     

Modeling and experiments of actively Q-switched Er/sup 3+/-Yb/sup 3+/ codoped clad-pumped fiber lasers

Two models are presented to describe the complex dynamics of Q-switched clad-pumped Er/sup 3+/-Yb/sup 3+/ codoped fiber lasers (EYDFLs): the full model that includes the full wavelength-dependence of parameters in the 1550- and the 1080-nm band due to Er/sup 3+/ and Yb/sup 3+/, respectively, and the simplified model that assumes single wavelengths for both bands. The models are based on detailed rate equations that include energy transfer between Er/sup 3+/ and Yb/sup 3+/ ions, and spontaneous emission due to both Er/sup 3+/ and Yb/sup 3+/. The simplified model is shown to agree with the full model within 10% difference. Experiments are performed using a 4-m-long single-mode clad-pumped EYDFL, and pulse energy of 14.5 /spl mu/J is achieved. Excellent agreement is shown between the simplified model and experiments. The model is further used to study the extractable energy of the laser and show limiting factors: amplified spontaneous emission (ASE) and energy storage in Yb/sup 3+/ ions. The model is also used to optimize the pulse energy in terms of fiber length, pump power, and Er/sup 3+/-Yb/sup 3+/ concentrations.     

High-f/sub max/ AlGaAs/InGaAs and AlGaAs/GaAs HBT's with p/sup +//p regrown base contacts

The present paper describes a new approach to fabricating high performance HBT's with low base resistance. Their base contact resistance is reduced by using MOMBE selective growth in the extrinsic base region-a key process in the fabrication of high-f/sub max/ AlGaAs/InGaAs and AlGaAs/GaAs HBT's. A p/sup +//p regrown base structure, which consists of a 40-nm-thick graded InGaAs strained layer and a heavily C-doped regrown contact layer, is used for the AlGaAs/InGaAs HBT's to reduce both their base transit time and base resistance, while preventing aluminum oxide incorporation at the regrowth interface. An h/sub fe/ of 93, an f/sub T/ of 102 GHz, and an f/sub max/ of 224 GHz are achieved for a 1.6-/spl mu/m/spl times/4.6-/spl mu/m HBT, together with reduced base push-out effects and improved reliability. AlGaAs/GaAs HBT's with an 80-nm-thick uniform base layer that have high f/sub max/ values ranging from 140-216 GHz are also fabricated using the selective growth technique. These results confirm the high potential of the proposed HBT's, especially for microwave and millimeter-wave applications.<>     

AlAs/AlGaAs的湿氧氧化及其在VCSEL制备中的应用

根据制备垂直腔面发射激光器 (VCSEL)电流限制层的需要 ,通过实验方法研究了氧化温度、Al组分和晶向等条件对AlGaAs氧化速率的影响 ,得到适用于VCSEL的材料参数和氧化条件 ;对氧化后表面分层、欧姆接触特性变差等现象进行分析 ,得到解决或改善方案。比较AlAs和Al0 .98Ga0 .0 2 As氧化特性及氧化后的热稳定性 ,结果表明Al0 .98Ga0 .0 2 As较AlAs更适于作VCSEL电流限制层。将优化的氧化条件及材料参数应用于VCSEL制备 ,得到室温连续工作的VCSEL器件 ,其阈值电流为 0 .8mA ,激射波长为 980nm ,工作电流为 15mA时输出功率可达 3.2mW。     

Performance of a high concentration Er/sup 3+/-doped alumino silicate fiber amplifier

We report the gain, noise figure, output saturation power, and conversion efficiency of a highly concentrated Er/sup 3+/-doped alumino silicate fiber amplifier. We obtain a gain per unit length of 1.0 dB/cm, which corresponds to the highest gain per unit length obtained in an Er/sup 3+/-doped fiber amplifier. The pump power threshold ranges from 2 to 5 mW, depending on the fiber length.     

S/sup 2/I: a switched-current technique for high performance

A new switched-current memory cell is presented which enhances basic cell performance through successive refinement of the memorised sample. This is achieved in a two-step technique, called S/sup 2/I, in which the input sample is coarsely memorised, a process which introduces a combination of all the normal errors followed by detection and suppression of the combined errors. The circuit solution requires the addition to the basic memory cell of only extra switches and so carries few of the penalties associated with alternative techniques.<>     

High-power 1.02 mu m InGaAs/AlGaAs strained quantum well lasers with GaInP buried waveguides for pumping Pr/sup 3+/-doped optical fibre amplifier

High power 1.02 mu m single spatial mode laser diodes with low-loss (3.3 cm/sup -1/) GaInP buried waveguides have been developed for pumping Pr/sup 3+/-doped optical fibre amplifiers. A maximum CW light output power of 415 mW and an optical fibre output of 71 mW at 200 mA have been achieved. A preliminary lifetest showed stable operation for over 2300 h under 100 mW CW conditions at 50 degrees C.<>     

Threshold voltage uniformity and characterization of microwaveperformance for GaAs/AlGaAs high electron-mobility transistors grown onSi substrates

We report on DC and microwave characteristics for high electron-mobility transistors (HEMT's) grown on Si substrates by metal-organic chemical vapor deposition (MOCVD). Threshold voltage (V _th) distribution in a 3-in wafer shows standard deviation of V_th (σV_th) of 36 mV with V_th of -2.41 V for depletion mode HEMT's/Si and σV_th of 31 mV with V_th of 0.01 V for enhancement mode, respectively. The evaluation of V_th in a 1.95×1.9 mm² area shows high uniformity for as-grown HEMT's/Si with σV_th of 9 mV for V_th of -0.10 V, which is comparable to that for HEMT's/GaAs. Comparing the V_th distribution pattern in the area with that for annealed HEMT's/Si, it is indicated that the high uniformity of V_th is obtained irrelevant of a number of the dislocations existing in the GaAs/Si. From microwave characteristic evaluation for HEMT's with a middle-(10~50 Ω·cm) and a high-(2000~6000 Ω·cm) resistivity Si substrate using a new equivalent circuit model, it is demonstrated that HEMT's/Si have the disadvantage for parasitic capacitances and resistances originated not from the substrate resistivity but from a conductive layer at the Si-GaAs interface. The parasitic parameters, especially the capacitances, can be overcome by the reduction of electrode areas for bonding pads and by the insertion of a dielectric layer under the electrode, which bring high cut-off frequency (f_T) and maximum frequency of operation (f_max) of 24 GHz for a gate length of 0.8 (μm). These results indicate that HEMT's/Si are sufficiently applicable for IC's and discrete devices and have a potential to be substituted for HEMT's/GaAs     

DC isolation and RF dissipation loss of coplanar waveguide on GaAs multi conductive Layers bombarded by H/sup +/ and Fe/sup +/ ions

This letter explores the dc isolation and radio frequency (RF) dissipation loss of coplanar waveguide (CPW) lines of H/sup +/ and Fe/sup +/ ion bombarded GaAs multi conductive epitaxial layers. It is demonstrated that although a sheet resistivity as high as 10/sup 8/ /spl Omega/sq has been achieved by ion bombardment, showing excellent dc isolation, the RF dissipation loss of gold metallized CPW lines on the bombarded multi conductive epitaxial layers are higher than that on a semi-insulating GaAs substrate, especially at higher frequencies (0.5 dB/cm higher at 50 GHz). This is probably caused by deep level trappings due to the ion bombardment.     

Scattering and electron mobility in combination-doped HFET-structures AlGaAs/InGaAs/AlGaAs with high electron density

Molecular-beam epitaxy is used for growing structures differing in doping technique and doping level and having a high two-dimensional-electron concentration n _s in the quantum well. The effect of doping combining uniform and δ doping on the electron-transport properties of heterostructures is investigated. A new type of structure with a two-sided silicon δ doping of GaAs transition layers located on the quantum-well boundaries is proposed. The largest value of electron mobility μ_H = 1520 cm²/(V s) is obtained simultaneously with a high electron density n _s = 1.37 × 10¹³ cm⁻² at 300 K with such a doping. It is associated with decreasing electron scattering by an ionized impurity, which is confirmed by the carried out calculations.     

Low dark current quasi-Schottky barrier MSM-photodiode structures on n-Ga/sub 0.47/In/sub 0.53/As with p/sup +/-Ga/sub 0.47/In/sub 0.53/As cap layer

The p/sup +/-cap layer was used to fabricate a metal-semiconductor-metal (MSM) interdigitated photodetector on Ga/sub 0.47/In/sub 0.53/As. The measured barrier height was Phi /sub Bn=/0.52 V, the ideality factor n=1.1 and average dark current density 2 mA/cm/sup 2/. A rise time of 45 ps at lambda =1.3 mu m under 2 V bias was measured for an MSM photodiode with 3 mu m finger width and finger gaps and an active area of 100*100 mu m/sup 2/.<>     

AlGaAs/InGaAs heterostructure doped-channel FET's exhibiting goodelectrical performance at high temperatures

High-power and high-efficiency GaAs heterostructure field-effect transistors (FETs) are attracting tremendous attention in RF power amplifier applications. However, thermal effects can be an important issue in RF power devices, owing to the huge amount of heat generated during their operation. In this paper, the temperature-dependent characteristics of Al_0.3Ga_0.7As/In_0.15Ga_0.85 As doped-channel FETs (DCFETs) are investigated and compared with conventional pseudomorphic-HEMTs (pHEMTs) devices, in terms of their dc, microwave and RF power performance at temperatures ranging from room temperature to 150°C. Due to conducting carriers being less influenced by temperature and the better Schottky diode characteristics that can be obtained in DCFETs, the intrinsic device parameters and output performance remain almost constant at high temperatures, which also results in better device reliability. The performance variation of DCFETs associated with temperatures from 25°C to 150°C all fall within a single digit, i.e., output power (P_out, 16.2 dBm versus 15.8 dBm), power gain (G_p, 16.6 dB versus 15.1 dB), power added efficiency (PAE, 34.2% versus 31.3%), which is not the case for conventional pHEMTs. Therefore, DC devices are very promising for microwave power device applications operating at high temperature     

cdma2000/sup /spl reg// high rate broadcast packet data air interface design

The Third Generation Partnership Project 2 recently baselined the specification for a cdma2000/sup /spl reg// high-rate broadcast packet data air interface ("cdma2000 High Rate Broadcast-Multicast Packet Data Air Interface Specification", 3GPP2 C.50054). The standard allows high-speed delivery of packet data to multiple access terminals. The article describes the air interface design adopted by 3GPP2, and presents simulation results that predict the performance of the high-speed broadcast system.     

S/N and error rate performance in AlGaAs semiconductor laser preamplifier and linear repeater systems

The applications of AlGaAs semiconductor laser preamplifier and linear repeaters in single mode optical fiber transmission systems were studied through the baseband signal-to-noise ratio and bit error rate performance measurement. Experiments were carried out with the Fabry-Perot cavity laser amplifiers whose characteristics are improved by reducing the input mirror reflectivity to 6 percent. The use of a preamplifier improves the minimum detectable power by 7.4 dB over the Si-APD direct detection level when the received signal is amplified by 30 dB before photodetection. The use of two linear repeaters increases the regenerative repeater gain by 37 dB. These experimental results are in good agreement with theoretical predictions based on the photon statistic master equation analysis.