High breakdown voltage (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P/InGaAs quasi-enhancement-mode pHEMT with field-plate technology

A high breakdown voltage and a high turn-on voltage (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P/InGaAs quasi-enhancement-mode (E-mode) pseudomorphic HEMT (pHEMTs) with field-plate (FP) process is reported for the first time. Between gate and drain terminal, the transistor has a FP metal of 1 /spl mu/m, which is connected to a source terminal. The fabricated 0.5/spl times/150 /spl mu/m/sup 2/ device can be operated with gate voltage up to 1.6 V owing to its high Schottky turn-on voltage (V/sub ON/=0.85 V), which corresponds to a high drain-to-source current (I/sub ds/) of 420 mA/mm when drain-to-source voltage (V/sub ds/) is 3.5 V. By adopting the FP technology and large barrier height (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P layer design, the device achieved a high breakdown voltage of -47 V. The measured maximum transconductance, current gain cutoff frequency and maximum oscillation frequency are 370 mS/mm, 22 GHz , and 85 GHz, respectively. Under 5.2-GHz operation, a 15.2 dBm (220 mW/mm) and a 17.8 dBm (405 mW/mm) saturated output power can be achieved when drain voltage are 3.5 and 20 V. These characteristics demonstrate that the field-plated (Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/In/sub 0.5/P E-mode pHEMTs have great potential for microwave power device applications.     

Investigation of indium doping and incorporation in AlGaAs/GaAs double-barrier resonant tunnelling structures

In doping and incorporation in the barrier layers of AlGaAs/GaAs double-barrier resonant tunnelling structures (DBRTSs) have been studied. It was found that the peak-to-valley current ratio (PVCR) can be improved by the proper amount of In doping. This is attributed to the improvement in the quality of the AlGaAs barrier layers due to the high surface migration rate of In atoms that reduces group III vacancies. Also pseudomorphic In/sub x/(Al/sub 0.5/Ga/sub 0.5/)/sub 1-x/As/GaAs (x=0.12) strained-layer DBRTSs have been fabricated by incorporating a sufficient amount of In into the AlGaAs barrier layers. PVCRs as high as 27.5 at 77 K have been obtained. This is the first realisation of such DBRTSs with lattice-mismatched quaternary barrier layers.<>     

Evaluation of multiquantum barriers in bulk double heterostructure visible laser diodes

Three bulk (Al/sub x/Ga/sub 1-x/)/sub 0.5/In/sub 0.5/P double heterostructure (DH) lasers were designed and fabricated to examine the effect of incorporating multiquantum barrier (MQB) structures. The first laser, used as a reference, has a conventional structure, while the remaining lasers include MQB structures, one designed to achieve a virtual barrier of 75 meV, the other having a transmission window up to 100 meV above the bulk barrier height. Measurements show a reduction of up to 31% in the room temperature threshold current and an increase in characteristic temperature of 20 K by the inclusion of the optimized MQB structure in comparison with the reference laser. However, since the leaky MQB design also shows a significant room temperature improvement over the reference laser we suggest that the device improvements produced by the MQB structures are not solely due to the formation of a virtual barrier.     

调制掺杂AlGaN/GaN异质结上的Pt肖特基接触

研究了调制掺杂 Alx Ga1 - x N/Ga N表面 Pt肖特基接触的制备工艺 ,并对其进行了 I-V测量。通过改变对样品表面的处理工艺 ,研究了表面处理对调制掺杂 Alx Ga1 - x N/Ga N表面 Pt肖特基结接触特性的影响 ,在 n型掺杂浓度为 7.5× 1 0 1 7cm- 3的 Al0 .2 2 Ga0 .78N样品表面 ,制备得到了势垒高度为 0 .94e V、理想因子为 1 .4的 Pt肖特基接触。这与国外报道的结果接近 (=1 .2 e V,n=1 .1 1 [1 ] )     

High power, 60 W quasi-CW, visible laser diode arrays

Visible spectrum diode arrays have been fabricated from (Al/sub x/Ga/sub 1-x/)/sub 0.5/In/sub 0.5/P-Ga/sub 0.4/In/sub 0.6/P quantum well heterostructures operating to high output powers at wavelengths of approximately 690 nm. Bars 7.5 mm long with 110 mu m broad area emitting apertures on 125 mu m centers have reached quasi-CW output powers of 60 W.<>     

Influence of Ni Schottky contact thickness on two-dimensional electron-gas sheet carrier concentration of strained AI0.3Ga0.7N/GaN heterostructures

Ni/Au Schottky contacts with thicknesses of either 50(A)/50(A) or 600 (A)/2000(A) were deposited on strained Al0.3Ga0.7N/GaN heterostructures.Using the measured C-V curves and Ⅰ-Ⅴ characteristics at room temperature,the calculated density of the two-dimensional electron-gas (2DEG) of the 600(A)/2000(A) thick Ni/Au Schottky contact is about 9.13 x 1012 cm-2 and that of the 50(A)/50(A) thick Ni/Au Schottky contact is only about 4.77 ×1012 cm-2.The saturated current increases from 60.88 to 86.34 mA at a bias of 20 V as the thickness of the Ni/Au Schottky contact increases from 50(A)/50(A)to 600(A)/2000(A).By self-consistently solving Schrodinger's and Poisson's equations,the polarization charge sheet density of the two samples was calculated,and the calculated results show that the polarization in the AIGaN barrier layer for the thick Ni/Au Schottky contact is stronger than the thin one.Thus,we attribute the results to the increascd biaxial tensile stress in the Al0.3Ga0.7N barrier layer induced by the 600(A)/2000(A)thick Ni/Au Schottky contact.     

MIM capacitors using atomic-layer-deposited high-/spl kappa/ (HfO/sub 2/)/sub 1-x/(Al/sub 2/O/sub 3/)/sub x/ dielectrics

Metal-insulator-metal (MIM) capacitors with (HfO/sub 2/)/sub 1-x/(Al/sub 2/O/sub 3/)/sub x/ high-/spl kappa/ dielectric films were investigated for the first time. The results show that both the capacitance density and voltage/temperature coefficients of capacitance (VCC/TCC) values decrease with increasing Al/sub 2/O/sub 3/ mole fraction. It was demonstrated that the (HfO/sub 2/)/sub 1-x/(Al/sub 2/O/sub 3/)/sub x/ MIM capacitor with an Al/sub 2/O/sub 3/ mole fraction of 0.14 is optimized. It provides a high capacitance density (3.5 fF//spl mu/m/sup 2/) and low VCC values (/spl sim/140 ppm/V/sup 2/) at the same time. In addition, small frequency dependence, low loss tangent, and low leakage current are obtained. Also, no electrical degradation was observed for (HfO/sub 2/)/sub 1-x/(Al/sub 2/O/sub 3/)/sub x/ MIM capacitors after N/sub 2/ annealing at 400/spl deg/C. These results show that the (HfO/sub 2/)/sub 0.86/(Al/sub 2/O/sub 3/)/sub 0.14/ MIM capacitor is very suitable for capacitor applications within the thermal budget of the back end of line process.     

Thermal stability of Al/AlGaAs and Al/GaAs/AlGaAs (MBE) Schottky barriers

Outstanding stability has been observed in Al/Al/sub x/Ga/sub 1-x/As and Al/GaAs/Al/sub x/Ga/sub 1-x/As (x=0.25) Schottky barriers prepared by depositing Al in situ by MBE on annealing up to 400 degrees C. Conventionally evaporated barriers have been fabricated and compared with epitaxial ones. The changes in barrier height and ideality factor induced by annealing are reported.<>     

The microwave power performance comparisons of Al/sub x/Ga/sub 1-x/As/In/sub 0.15/Ga/sub 0.85/As (x=0.3, 0.5, 0.7, 1.0) doped-channel HFETs

The properties of doped-channel field-effect transistors (DCFET) have been thoroughly investigated on Al/sub x/Ga/sub 1-x/As/InGaAs (x= 0.3, 0.5, 0.7, 1) heterostructures with various Al mole fractions. In this study, we observed that by introducing a 200-/spl Aring/-thick Al/sub 0.5/Ga/sub 0.5/As (x=0.5) Schottky layer can enhance the device power performance, as compared with the conventional x=0.3 AlGaAs composition system. However, a degradation of the device power performance was observed for further increasing the Al mole fractions owing to their high sheet resistance and surface states. Therefore, Al/sub 0.5/Ga/sub 0.5/As Schottky layer design provides a good opportunity to develop a high power device for power amplifier applications.     

Modeling of tunneling currents through HfO/sub 2/ and (HfO/sub 2/)/sub x/(Al/sub 2/O/sub 3/)/sub 1-x/ gate stacks

We present a physical modeling of tunneling currents through ultrathin high-/spl kappa/ gate stacks, which includes an ultrathin interface layer, both electron and hole quantization in the substrate and gate electrode, and energy band offsets between high-/spl kappa/ dielectrics and Si determined from high-resolution XPS. Excellent agreements between simulated and experimentally measured tunneling currents have been obtained for chemical vapor deposited and physical vapor deposited HfO/sub 2/ with and without NH/sub 3/-based interface layers, and ALD Al/sub 2/O/sub 3/ gate stacks with different EOT and bias polarities. This model is applied to more thermally stable (HfO/sub 2/)/sub x/(Al/sub 2/O/sub 3/)/sub 1-x/ gate stacks in order to project their scalability for future CMOS applications.     

Silica-clad neodymium-doped lanthanum phosphate fibers and fiber lasers

We have fabricated a neodymium-doped phosphate glass fiber with a silica cladding and used it to form a fiber laser. Phosphate and silicate glasses have considerably different glass transition temperatures and softening points making it hard to draw a fiber from these two glasses. A bulk phosphate glass of composition (Nd/sub 2/O/sub 3/)/sub 0.011/(La/sub 2/O/sub 3/)/sub 0.259/(P/sub 2/O/sub 5/)/sub 0.725/(Al/sub 2/O/sub 3/)/sub 0.005/ was prepared and the resultant material was transparent, free from bubbles and visibly homogeneous. The bulk phosphate glass was drawn to a fiber while being jacketed with silica and the resultant structure was of good optical quality, free from air bubbles and major defects. The attenuation at a wavelength of 1.06 /spl mu/m was 0.05 dB/cm and the refractive index of the core and cladding at the pump wavelength of 488 nm was 1.56 and 1.46, respectively. The fibers were mechanically strong enough to allow for ease of handling and could be spliced to conventional silica fiber. The fibers were used to demonstrate lasing at the /sup 4/F/sub 3/2/-/sup 4/I/sub 11/2/ (1.06 /spl mu/m) transition. Our work demonstrates the potential to form silica clad optical fibers with phosphate cores doped with very high levels of rare-earth ions (27-mol % rare-earth oxide).     

Highly reliable GaN-based light-emitting diodes formed by p-In/sub 0.1/Ga/sub 0.9/N-ITO structure

Indium-tin-oxide (ITO) is deposited as a transparent current spreading layer of GaN-based light-emitting diodes (LEDs). To reduce the interfacial Schottky barrier height, a thin p-In/sub 0.1/Ga/sub 0.9/N layer is grown as an intermediate between ITO and p-GaN. The contact resistivity around 2.6/spl times/10/sup -2/ /spl Omega//spl middot/cm/sup 2/ results in a moderately high forward voltage LED of 3.43 V operated at 20 mA. However, the external quantum efficiency and power efficiency are enhanced by 46% and 36%, respectively, in comparison with the conventional Ni-Au contact LEDs. In the life test, the power degradation of the p-In/sub 0.1/Ga/sub 0.9/N-ITO contact samples also exhibits a lower value than that of the conventional ones.     

High-breakdown characteristics of the InP-based heterostructurefield-effect transistor withIn0.34Al0.66As0.85Sb0.15Schottky layer

We report improved breakdown characteristics of InP-based heterostructure field-effect transistors (HFET's) utilizing In_0.34 Al_0.66As_0.85Sb_0.15 Schottky layer grown by low-pressure metalorganic chemical vapor deposition. Due to high energy bandgap and high Schottky barrier height (>0.73 eV) of the In_0.34Al_0.66As_0.85Sb_0.15 Schottky layer, high two-terminal gate-to-drain breakdown voltage of 40 V, three-terminal off-state breakdown voltage of 40 V three-terminal threshold-state breakdown voltage of 31 V, and three-terminal on-state breakdown voltage of 18 V at 300 K for In_0.75Ga_0.25As channel, are achieved. Moreover, the temperature dependence of two-terminal reverse leakage current is also investigated. The two-terminal gate-to-drain breakdown voltage is up to 36 V at 420 K. A maximum extrinsic transconductance of 216 mS/mm is obtained with a gate length of 1.5 μm     

Calculated threshold currents of nitride- and phosphide-based quantum-well lasers

We have calculated the room temperature gain-current characteristics for a 360 nm wavelength, 80 /spl Aring/ GaN-Al/sub 0.14/Ga/sub 0.86/N and a red-emitting, 80 /spl Aring/ Ga/sub 0.51/In/sub 0.49/P-(Al/sub 0.44/Ga/sub 0.56/)/sub 0.51/In/sub 0.49/P quantum well laser structures, including many body effects. Although the carrier density and spontaneous current are much higher (by a factor of 4 and 3, respectively) in the nitride structures for a given local gain, the higher confinement factor at short wavelengths means the intrinsic threshold current of these devices is predicted to be approximately twice that of red lasers with the same optical loss.     

Effect of the post-gate annealing on the gate reliability of AlGaN/GaN HEMTs

In this paper,we investigated the effect of post-gate annealing (PGA) on reverse gate leakage and the reverse bias reli-ability of Al0.23Ga0.77N/GaN high electron mobility transistors (HEMTs).We found that the Poole-Frenkel (PF) emission is domin-ant in the reverse gate leakage current at the low reverse bias region (Vth ＜ VG ＜ 0 V) for the unannealed and annealed HEMTs.The emission barrier height of HEMT is increased from 0.139 to 0.256 eV after the PGA process,which results in a reduction of the reverse leakage current by more than one order.Besides,the reverse step stress was conducted to study the gate reliabil-ity of both HEMTs.After the stress,the unannealed HEMT shows a higher reverse leakage current due to the permanent dam-age of the Schottky gate.In contrast,the annealed HEMT shows a little change in reverse leakage current.This indicates that the PGA can reduce the reverse gate leakage and improve the gate reliability.     

Thermal reliability and performances of InGaP schottky contact with Cu/Au and Au/Cu-MSM photodetectors

We report the Schottky performance and thermal reliability of a wide bandgap InGaP layer in contact with a Cu/Au metallic system. An effective Schottky barrier height of 0.97 eV and an ideality factor of 1.21 can be achieved. The thermal reliability of the resultant Schottky barrier diodes was analyzed using Auger electron spectroscopy and atomic force microscopy. The thermal reliability could be main tained up to 450°C. The failure mechanism was attributable to the decomposition of the InGaP layer and the interdiffusion of the chemical elements at higher temperature. Insensitive photoresponsivity with the in cident optical power was found for the resultant Au/Cu-metal-semiconductor-metalphotodetectors (MSM-PDs). According to the measured temporal response of the Au/Cu-MSM-PDs, the operation frequency could be above 10 GHz.     

Analysis of Schottky Barrier Height in Small Contacts Using a Thermionic‐Field Emission Model

This paper reports on estimating the Schottky barrier height of small contacts using a thermionic‐field emission model. Our results indicate that the logarithmic plot of the current as a function of bias voltage across the Schottky diode gives a linear relationship, while the plot as a function of the total applied voltage across a metal‐silicon contact gives a parabolic relationship. The Schottky barrier height is extracted from the slope of the linear line resulting from the logarithmic plot of current versus bias voltage across the Schottky diode. The result reveals that the barrier height decreases from 0.6 eV to 0.49 eV when the thickness of the barrier metal is increased from 500 Å to 900 Å. The extracted impurity concentration at the contact interface changes slightly with different Ti thicknesses with its maximum value at about 2.9×10²⁰ cm^?3, which agrees well with the results from secondary ion mass spectroscopy (SIMS) measurements.     

Asymmetric Schottky Contacts in Bilayer MoS2 Field Effect Transistors

The high‐bias electrical characteristics of back‐gated field‐effect transistors with chemical vapor deposition synthesized bilayer MoS₂ channel and Ti Schottky contacts are discussed. It is found that oxidized Ti contacts on MoS₂ form rectifying junctions with ≈0.3 to 0.5 eV Schottky barrier height. To explain the rectifying output characteristics of the transistors, a model is proposed based on two slightly asymmetric back‐to‐back Schottky barriers, where the highest current arises from image force barrier lowering at the electrically forced junction, while the reverse current is due to Schottky‐barrier‐limited injection at the grounded junction. The device achieves a photoresponsivity greater than 2.5 A W^?1 under 5 mW cm^?2 white‐LED light. By comparing two‐ and four‐probe measurements, it is demonstrated that the hysteresis and persistent photoconductivity exhibited by the transistor are peculiarities of the MoS₂ channel rather than effects of the Ti/MoS₂ interface.     

Sheet resistance measurement of non-standard cleanroom materials using suspended Greek cross test structures

This paper presents work on the development, fabrication and characterization of a suspended Greek cross measurement platform that can be used to determine the sheet resistance of materials that would contaminate Complementary Metal Oxide Semiconductor (CMOS) processing lines. The arms of the test structures are made of polysilicon/silicon nitride (Si/sub 3/N/sub 4/) to provide a carrier for the film to be evaluated and thick aluminum (Al) probe pads for multiple probing. The film to be evaluated is simply blanket deposited onto the structures and because of its design automatically forms a Greek cross structure with (Al) probe pads. To demonstrate its use, 1) gold (Au), 2) copper (Cu), and 3) silver(Ag) loaded chalcogenide glass Ag/sub y/(Ge/sub 30/Se/sub 70/)/sub 1-y/ have been blanket evaporated in various thicknesses onto the platform in the last processing step and autopatterned by the predefined shape of the Greek crosses. The suspension of the platform ensured electrical isolation between the test structure and the surrounding silicon (Si) substrate. The extracted effective resistivity for Au (5.1/spl times/10/sup -8/ /spl Omega//spl middot/m), Cu (1.8- 2.5/spl times/10/sup -8//spl bsol/ /spl Omega//spl middot/m) and Ag/sub y/(Ge/sub 30/Se/sub 70/)/sub 1-y/ (2.27/spl times/10/sup -5/ /spl Omega//spl middot/m-1.88 /spl Omega//spl middot/m) agree with values found in articles in the Journal of Applied Physics (1963), the Journalof Physics D: Applied Physics (1976), and the Journalof Non-Crystalline Solids (2003). These results demonstrate that the proposed Greek cross platform is fully capable to measure the sheet resistance of low (Au, Cu) and high Ag/sub y/(Ge/sub 30/Se/sub 70/)/sub 1-y/ resistive materials.     

6H-SiC Schottky二极管的正向特性

提出了一种考虑Schottky结势垒不均匀性和界面层作用的Si C Schottky二极管( SBD)正向特性模型,势垒的不均匀性来自于Si C外延层上的各种缺陷,而界面层上的压降会使正向Schottky结的有效势垒增高.该模型能够对不同温度下Si C Schottky结正向特性很好地进行模拟,模拟结果和测量数据相符.它更适用于考虑器件温度变化的场合,从机理上说明了理想因子、有效势垒和温度的关系.