Quantum-well-doped FET (QUD-FET)

A novel FET using a 2DEG is presented. The FET has an AlAs/GaAs/AlAs single quantum well with planar doping in the centre of the GaAs layer. The conduction channels are composed of a 2DEG generated in undoped GaAs layers outside the well. The measured 2DEG concentration was 1.8?2 × 1012cm?2 with electron mobilities of 3500cm2/Vs at RT and 10500cm2/Vs at 77K. A 1.5?m-gate-length FET exhibits a maximum transconductance of 174 mS/mm and a maximum current exceeding 300 mA/mm at 77K.     

量子限制效应对受主跃迁的影响

通过光致发光光谱,研究了量子限制效应对GaAs体材料中均匀掺杂和一系列GaAs/AlAs多量子阱(阱宽范围从30A到200A)中δ-掺杂浅受主杂质铍(Be)原子带间跃迁的影响.实验中所用的样品是利用分子束外延技术生长的均匀掺Be受主的GaAs外延层和一系列在量子阱的中央进行了浅受主Be原子δ-掺杂的GaAs/AlAs多量子阱.在4.2K的低温下,测量了上述样品的光致发光谱,很清楚地观察到了受主束缚激子从基态1S3/2(Γ6)到两个激发态2S3/2(Γ6)和3S3/2(Γ6)的双空穴跃迁.研究发现,随着量子限制效应的增强,受主跃迁能量会增加.对量子限制效应调节受主杂质问跃迁能量的研究,进一步增强了对受主能态可调性的认识,为太赫兹远红外发光器或激光器的研发提供了一种新的途径.     

Effect of Si3N4 encapsulation on the laser-annealing behaviour of GaAs

When semi-insulating GaAs samples are coated with pyrolytically deposited Si3N4 layers and subsequently irradiated with a Q-switched ruby laser with energy densities > 0.3 J/cm2, it is found that a thin layer (0.1?0.25 ?m) of the underlying GaAs substrates becomes n-type. This phenomenon may be the reason why, in previous work on laser annealing of donor implanted GaAs samples, the percentage electrical activity increased when samples were coated with Si3N4.     

Laser Annealed and Thermal Annealed Refractory Ohmic Contacts to GaAs

Ohmic contacts to n-type GaAs have been developed for high-temperature device applications up to 300°C. Refractory metallizations were used with epitaxial Ge layers to form the contacts TiW/Ge/GaAs, Ta/Ge/GaAs, Mo/Ge/GaAs, and Ni/Ge/GaAs. Contacts with high dose Si or Se ion implantation (1012 to 1014/cm2) of the Ge/GaAs interface were also investigated. The purpose of this work was to develop refractory ohmic contacts with low specific-contact resistance (~10-6 ?cm2 on 1 x 1017cm-3GaAs) which are free of imperfections, resulting in a uniform n+ doping layer. The contacts were fabricated on epitaxial GaAs layers (n = 2 x 1016 to 2 x 1017 cm-3) grown on n+ ( 2 x 1018 cm-3) or semi-insulating GaAs (at strates. Ohmic contact was formed by both thermal annealing ( at temperatures up to 700°C) and laser annealing (pulsed Ruby). Examination of the Ge/GaAs interface revealed Ge migration into GaAs to form an n+layer. Under optimum laser anneal conditions, the specific contact resistance was in the range 1-5 x 10-6 ?-cm2 (on 2 x 1017cm-3GaAs). Thermally annealed TiW/Ge had a contact resitivity of 1 x 10-6 ? cm2 on 1 x 1017 cm-3 GaAs under optimum anneal conditions. The contacts also showed improved thermal stability over conventional Ni/AuGe contacts at temperatures above 300°C.     

Broadband GaAs FET optical front-end circuit up to 5.6 GHz

Design and performance of transimpedance preamplifiers for multi-gigabit/s optical repeaters are reported using 0.3 ?m gate length GaAs FETs and a Ge-APD with a sensitive area of 30 ?m diameter. Through reduction of parasitic inductance and stray capacitance in chip assembly, a 3 dB down bandwidth of 8.2 GHz is achieved without a Ge-APD. A 3 dB down bandwidth of 5.6 GHz and good pulse response to 6.5 Gbit/s RZ pattern optical signals are achieved in an optical front-end circuit with a Ge-APD.     

On the spectra of electrons and holes in an open spherical nanoheterostructure (through the example of GaAs/AlxGa1−x As/GaAs)

The spectra of the quasi-stationary electron and hole states in an open spherical nanoheterostructure are calculated in the effective mass approximation using the S-matrix theory. Numerical calculation is performed through the example of the GaAs/Al_xGa_1?x As/GaAs system. A complete system of electron and hole wave functions is obtained for nanoheterostructures consisting of an arbitrary number of layers. Quasiparticle lifetimes as a function of the GaAs/Al_xGa_1?x As/GaAs nanosystem geometrical parameters and Al content x are calculated.     

Ultra low resistance ohmic contacts to n-GaAs

Nonalloyed ohmic contacts to n-GaAs with contact resistances (?c) below 1·0×10?7 ? cm2 have been obtained using a Ge/GaAs heterojunction system. Metals are evaporated on heavily arsenic-doped germanium (Ge) layers grown on GaAs. Low values of ?c result from the low Schottky barrier height (? 0·50 eV) and the high doping levels obtainable for n-Ge(? 1020 cm?3).     

Modelling the 3rd-order intermodulation-distortion properties of a GaAs f.e.t.

A simple analytical model of the 3rd-order intermodulation-distortion properties of a GaAs field-effect transistor is proposed. The model takes into account the distortion-producing nonlinearities of the Schottky-bairier junction, the trans-conductance and the drain conductance. Parameters of the model are presented for a GaAs f.e.t. of 0.5 ?m gate length, and the model-predicted distortion characteristics are compared with measured data.     

Stable monolithic GaAs FET oscillator

A monolithic X-band GaAs FET oscillator has been developed. Passive circuit components are lumped capacitors and inductors on semi-insulating GaAs; the chip size is 1.2 × 1.4 mm2. Stabilised with a Ba2Ti9O20 dielectric resonator, the oscillator delivers more than 30 mW output power at 10.8 GHz with a maximum chip efficiency of 20%. The frequency drift is better than 1 × 10?6/K from ?20°C to 80°C.     

Wideband monolithic GaAs amplifier using cascodes

A monolithic matched, two-stage wideband amplifier with an insertion gain of 26dB and a ? 3dB bandwidth of 3-2GHz is reported. Optimally designed cascode circuits are used to enhance the gain-bandwidth product available per stage. The IC has been fabricated in a I? depletion GaAs MESFET technology.     

High-efficiency GaAs power MESFETs prepared by ion implantation

GaAs power MESFETs have been fabricated using ion implantation to form channel layers. A 1 ?m gate length by 2400 ?m gate width device has demonstrated an output power of 1.63 W with 6.9 dB associated gain, 35% power-added efficiency and 9.7 dB linear gain at 10 GHz. The transconductance of this device is 280 mS, which corresponds to 117 mS/mm. This result demonstrates that excellent GaAs power MESFETs can be made by ion implantation, and is comparable to average results demonstrated by devices made by AsCl3 vapour phase epitaxy.     

Very low threshold current densities (under 100 A/cm2) in AlGaAs/GaAs single-quantum-well GRINSCH lasers grown by molecular beam epitaxy

Threshold current densities as low as 80 A/cm2 for 3.3 mm-long cavity lasers, and 93 A/cm2 for 520 ?m-long cavity lasers have been obtained in AlGaAs/GaAs graded-index separate-confinement heterostructure (GRINSCH) single-quantum-well lasers with quantum-well widths between 65?165 A grown by molecular beam epitaxy. The structures were prepared on (100) GaAs substrates and do not display the earlier reported dependence of lasing threshold characteristics on the quantum-well thickness in the range studied (65?165 A).     

Monolithically integrated, photoreceiver with large, gain-bandwidth product

A direct-detection 800 nm GaAs monolithically integrated photoreceiver is reported with a photocurrent gain of 200 and a 1 GHz bandwidth capable of driving a 50 ? load with IV peak pulses. The integrated NPN photodiode has over 7GHz bandwidth and requires no modifications to the ion-implanted GaAs MESFET process. The 200GHz gain-bandwidth product and 3200 V/W responsivity are among the highest reported for similar receivers.     

Ga0.47In0.53As field-effect transistors with a lattice-mismatched reduced leakage current GaAs gate

A lattice-mismatched GaAs gate Ga0.47In0.47As field-effect transistor (LMG-FET) with significantly reduced reverse gate leakage current is reported. The mechanism responsible for this reduction by over two orders of magnitude over previous work has been identified; it is attributed to the confinement of misfit dislocations originating at the GaAs/InGaAs interface. The LMG-FET had a gate leakage current of 0.48 ?A at ? V, and an extrinsic DC transconductance of 104 mS/ mm for a 1.4 ?m gate length and 240 ?m gate width. Further refinements in crystal growth should lead to even lower values of leakage current, making this technology attractive for high-speed logic, as well as lightwave optoelectronic integration.     

GaAs-GaAlAs anti-Stokes light convertor

A multilayer heterojunction device has been manufactured and used for efficient anti-Stokes light conversion. The device consists of six layers: p GaAs, n GaAs, n GaxAl1?xAs, p GayAl1?yAs, p GaxAl1?xAs and p GaAs, essentially forming a GaAs photodiode coupled with a GaAlAs l.e.d. Avalanche multiplication of photoexcited carriers is used to increase the l.e.d. driving current.     

High mobility GaAs-AlxGa1?xAs single period modulation-doped heterojunctions

Single period modulation-doped structures composed of an AlxGa1?xAs layer, part of which is doped with Si, on top of an undoped GaAs layer have been grown by molecular beam epitaxy. The films were characterised using Hall effect measurements carried out at temperatures between 10 and 300 K. With 50?75 ? thick undoped (Al, Ga)As layers near the interface, mobilities in excess of 115000 cm2/Vs at 10 K and 7450 cm2/Vs at 300 K have been achieved for an average doping concentration of ?5×1016 cm?3. These are some of the highest mobilities as yet obtained from modulation-doped structures, and represent an increase in mobility over equivalently doped GaAs by about a factor of 20 at 10 K and by a factor of 2 at 300 K.     

1.5 GHz operation of an AlxGa1?xAs/GaAs modulation-doped photoconductive detector

We demonstrate a planar AlxGa1?xAs/GaAs modulation-doped photoconductive detector operating at frequencies up to 1.5 GHz. This detector exhibits a peak responsivity of 2 A/W at these operating conditions, which corresponds to a gain of 3. We found that the peak responsivity increased with reduced pulse repetition rates, reaching 5 A/W at 1 MHz. We also measured the noise power at 800 MHz. This investigation suggests that the detector can be useful for shortwavelength (? ? 0.82 ?m) giga-bit-rate integrated photoreceiver applications.     

Optimisation of modulation-doped heterostructures for TEGFET operation at room temperature

Optimisation of selectively doped (AlGa)As/GaAs heterostructures for TEGFET applications at room temperature is reported. The introduction of a thick (>0.1 ?m) highly doped GaAs top layer considerably reduces parasitic resistances and improves device performance. Best results for 1.4 ?m gate length at room temperature are: transconductance 220 mS/mm; source resistance 0.2?0.4 mm; contact resistance less than 0.1 ? mm and cutoff frequency 25 GHz. Results from comparable structures without a thick top layer are inferior by about 25%.     

Reproducible low-resistivity AuMn ohmic contact for p-type GaAs

A novel ohmic contact 96% Au-4% Mn has been established for p-type GaAs. A specific contact resistivity of 2 × 10?7 ?cm2 has been obtained on 2 × 1019 cm?3 epitaxial layers after alloying, and a resistivity of 2 × 10?6 ?cm2 has been obtained on 2 × 1020 cm?3 doped layers without alloying. The contact is stable and reproducible.     

Reduced light sensitivity and persistent photoconductivity in novel modulation doped heterostructures incorporating an n·GaAs/AlGaAs superlatt1ce as the high bandgap material

A short period 15 Å/15 Å GaAs/Al_xGa_1?xAs superlattice where only the GaAs layers are doped with Si donors has been incorporated in a GaAs/Al_xGa_1?xAs molecular beam epitaxial modulation doped heterostructure in place of the doped high bandgap ternary alloy. The removal of the donors from the Al_xGa_1?xAs eliminates the component of light sensitivity resulting from the deep persistent photoconductivity (PPC) traps present in this material. This results in a reduction in overall light sensitivity and an elimination of the PPC effect at 77K.