SOI technology for radio-frequency integrated-circuit applications

This paper presents a silicon-on-insulator (SOI) integration technology, including structures and processes of OFF-gate power nMOSFETs, conventional lightly doped drain (LDD) nMOSFETs, and spiral inductors for radio frequency integrated circuit (RFIC) applications. In order to improve the performance of these integrated devices, body contact under the source (to suppress floating-body effects) and salicide (to reduce series resistance) techniques were developed for transistors; additionally, locally thickened oxide (to suppress substrate coupling) and ultra-thick aluminum up to 6 /spl mu/m (to reduce spiral resistance) were also implemented for spiral inductors on high-resistivity SOI substrate. All these approaches are fully compatible with the conventional CMOS processes, demonstrating devices with excellent performance in this paper: 0.25-/spl mu/m gate-length offset-gate power nMOSFET with breakdown voltage (BV/sub DS/) /spl sim/ 22.0 V, cutoff frequency (f/sub T/)/spl sim/15.2 GHz, and maximal oscillation frequency (f/sub max/)/spl sim/8.7 GHz; 0.25-/spl mu/m gate-length LDD nMOSFET with saturation current (I/sub DS/)/spl sim/390 /spl mu/A//spl mu/m, saturation transconductance (g/sub m/)/spl sim/197 /spl mu/S//spl mu/m, cutoff frequency /spl sim/ 25.6 GHz, and maximal oscillation frequency /spl sim/ 31.4 GHz; 2/5/9/10-nH inductors with maximal quality factors (Q/sub max/) 16.3/13.1/8.95/8.59 and self-resonance frequencies (f/sub sr/) 17.2/17.7/6.5/5.8 GHz, respectively. These devices are potentially feasible for RFIC applications.     

Low-light-level photoconductivity in semi-insulating GaAs

A peculiar photoconductive property with a positive temperature coefficient in a semi-insulating GaAs photodiode is found in the room temperature range. Also, the low-light-level photoconductivity is higher than usual. The authors suggest that an ionised-impurity scattering mechanism is dominant. Theoretical responsivity is compared with the measured value.<>     

Growth and characterization of large diameter undoped semi-insulating GaAs for direct ion implanted FET technology

The growth of large diameter, semi-insulating GaAs crystals of improved purity by Liquid Encapsulated Czochralski (LEC) pulling from pyrolytic boron nitride (PBN) crucibles and characterization of this material for direct ion implantation technology, is described. Three-inch diameter, 〈100〉-oriented GaAs crystals have been grown in a high pressure Melbourn crystal puller using 3 kg starting charges synthesized in-situ from 6/9s purity elemental gallium and arsenic. Undoped and Cr-doped LEC GaAs crystals pulled from PBN crucibles exhibit bulk resistivities in the 10⁷ and 10⁸ Ω cm range, respectively. High sensitivity secondary ion mass spectrometry (SIMS) demonstrates that GaAs crystals grown from PBN crucibles contain residual silicon concentrations in the mid 10¹⁴ cm^?3 range, compared to concentrations up to the 10¹⁶ cm^?3 range for growths in fused silica containers. The residual chromium content in undoped LEC grown GaAs crystals is below the SIMS detection limit for Cr (4 × 10¹⁴ cm^?3).The achievement of direct ion implanted channel layers of near-theoretical mobilities is further evidence of the improved purity of undoped, semi-insulating GaAs prepared by LEC/PBN crucible techniques. Direct implant FET channels with (1–1.5) × 10¹⁷ cm^?3 peak donor concentrations exhibit channel mobilities of 4,800–5,000 cm²/V sec in undoped, semi-insulating GaAs substrates, compared with mobilities ranging from 3,700 to 4,500 cm²/V sec for various Cr-doped GaAs substrates. The concentration of compensating acceptor impurities in semi-insulating GaAs/PBN substrates is estimated to be 1 × 10¹⁶ cm^?3 or less, and permits the implantation of 2 × 10¹⁶ cm^?3 channels which exhibit mobilities of 5,700 and 12,000 cm²/V sec at 298K and 77K, respectively.Discrete power FET's which exhibit 0.7 watts/mm output and 8 dB associated gain at 8 GHz have been fabricated using these directly implanted semi-insulating GaAs substrates.     

Filamentary injection currents in semi-insulating GaAs

Current filaments have been observed in the post-breakdown region of two-carrier space-charge-limted diodes in silicon and gallium arsenide. An analytical expression for the radial distribution of current in such filaments has been derived using an appropriate model for the total current-electric field problem. This derived expression is solved numerically for semi-insulating GaAs. These analytical results are compared with the experimental observations.     

High-speed Schottky photodiode on semi-insulating GaAs

A high-speed GaAs photodiode has been fabricated on a GaAs semi-insulating substrate. The photodiode has an active area of 8 ?m × 15 ?m and a bandwidth in excess of 9 GHz. This Schottky photodiodes is suitable for monolithic integration with other optoelectronic components.     

Characterization of horizontal Bridgman-grown semi-insulating GaAs for ion implantation

Thermal stability of horizontal Bridgman-grown (HB) Cr-doped seme-insulating GaAs is characterized systematically by leakage current measurement. Electrical characteristics for a Si-ion implanted n-layers on GaAs were evaluated by Hall and C-V measurements. The threshold voltage uniformity for MESFETs fabricated on implanted n-layer was also discussed. Not only the leakage current of annealed wafers but also the electrical properties of the ion implanted n-layers have a close correlation with the Cr concentration in the bulk GaAs. The uniformity of the ion implanted n-layer was degraded by the Cr concentration variations in the wafer. In addition to uniformity, mobility data, which show lower values for HB crystals than for undoped LEC crystal, imply the importance of high purity GaAs semi-insulating LEC crystal.     

Thermally stimulated current spectroscopy of high-purity semi-insulating 4H-SiC substrates

High-purity semi-insulating (HPSI) 4H-SiC has been widely used as a substrate material for AlGaN/GaN high electron-mobility transistors because of its fairly good lattice match with GaN and its high thermal conductivity. To control material quality, it is important to understand the nature of the deep traps. For this purpose, we have successfully applied thermally stimulated current (TSC) spectroscopy to investigate deep traps in two HPSI 4H-SiC samples grown by physical vapor transport (PVT) and high-temperature chemical vapor deposition (HTCVD), respectively. Fundamentals of TSC spectroscopy, typical TSC spectra obtained on the two samples, and theoretical fittings of a boron-related trap (peaked at ∼ 150 K) will be presented. Based on literature data for deep traps in conductive 4H-SiC, the impurity and point-defect nature of several commonly observed TSC traps, peaked at ∼105 K (0.22 eV), ∼150 K (0.29 eV), ∼175 K (∼0.33 eV), ∼260 K (∼0.53 eV), ∼305 K (∼0.63 eV), and ∼360 K (0.91 eV), in the HPSI 4H-SiC will be discussed.     

P-type anode structure for GaAs TEDs on semi-insulating substrate

The use of a p-type anode in a planar GaAs Gunn device was studied for the first time. The undesirable decrease of current for dc bias, compared with pulsed bias, is eliminated by hole injection to the overcritically doped n-layer from a p-n junction anode. These devices have exhibited satisfactory Gunn domain operation for triggered dc operation.     

Whole-ingot annealed semi-insulating GaAs substrates for low-noise microwave amplifiers

The quality of liquid-encapsulated Czochralski (LEC) grown GaAs substrates critically affects the final low-noise microwave device and circuit performance as evidenced by comparing Si-implanted undoped, In-alloyed, and whole-ingot annealed semi-insulating substrates. We investigated differences in Si-implant activation, electrical profiles, and uniformity of material, device, and circuit parameters. The best noise figure of 1.33 dB at 10 GHz was measured on a 0.5-µm low-noise FET fabricated on the high-pressure whole-ingot annealed LEC wafer. A noise figure of 2.0 dB with associated gain of 24 dB at 10 GHz was achieved for a monolithic two-stage low-noise amplifier (LNA) fabricated on the standard high-pressure LEC substrate.     

High-purity semi-insulating GaAs material for monolithic microwave integrated circuits

Liquid-Encapsulated Czochralski (LEC) growth of large-diameter bulk GaAs crystals from pyrolytic boron nitride (PBN) crucibles has been shown to yield high crystal purity, stable high resistivities, and predictable direct ion-implantation characteristics. Undoped (≲low 10¹⁴cm^-3chromium) and lightly Cr-doped (low 10¹⁵cm^-3range) -GaAs crystals, synthesized and pulled from PBN crucibles contain residual shallow donor impurities typically in the mid 10¹⁴cm^-3, exhibit bulk resistivities above 10⁷Ω . cm, and maintain the high sheet resistances required for IC fabrication (>10⁶Ω/□) after implantation anneal. Direct²⁹Si channel implants exhibit uniform (± 5 percent) and predictable LSS profiles, high donor activation (75 percent), and 4800- to 5000-cm²/V . s mobility at the (1 to 1.5) × 10¹⁷cm^-3peak doping utilized for power FET's. It has also been established that LEC crystals can provide the large-area, round     

The roles of the surface and bulk of the semi-insulating substrate in low-frequency anomalies of GaAs integrated circuits

We investigate in detail two anomalies in metal-semiconductor field-effect transistors (MESFET) which are detrimental to their operation in a GaAs integrated circuit (IC). The first of these is side-gating and consists in a parasitic very-low-frequency transconductance between a MESFET and an isolated electrode or side gate sharing the same semi-insulating (SI) substrate. The second anomaly is kinetic and consists in a parasitic transient in the drain-source current following an abrupt change in drain-source voltage. The time constants of the transients are observed to be very sensitive to the side-gate electrode potential. The effects of different technological and operational parameters are studied. One surprising result is the very high sensitivity of side-gating to chemical wet and dry treatments and to dielectric encapsulation of the unprotected substrate surfaces. We also report low-frequency oscillations related to side-gating. Physical models are proposed and yield consistent interpretations of our experimental observations.     

Space-charge-limited triode using a Cr-doped semi-insulating GaAs

By providing ohmic contacts and a rectifying contact to a Cr-doped semi-insulating GaAs material, triode-like device characteristics were experimentally verified. The current drawn through the device is interpreted as space-charge-limited current (SCLC). Operation of the device is shown to be qualitatively in agreement with the vacuum triode analog.     

Edge-photoluminescence concentration dependence in semi-insulating undoped GaAs

Dependences of the spectral peak position of edge photoluminescence, its half-width, resistivity, charge carrier mobility in crystals of semi-insulating undoped GaAs on the carbon concentration N _C at 77 K (3.0×10¹⁵ cm^?3≤N _C≤4.3×10¹⁶ cm^?3) were studied. The dependences observed are explained by the interaction of charge carriers with ionized impurity atoms and with structural defects.     

半绝缘GaAs倍频效应的研究

理论研究了GaAs的倍频效应,当基频光电场的偏振方向沿[111]方向时,倍频效应最显著;当基频光垂直于半球形GaAs样品的(001)底面入射时,产生的二次谐波沿(001)面传播.首次从光电流随基频光偏振方向的变化这一角度验证了波长为1.3μm的基频光沿GaAs晶体的[001]方向入射时的倍频吸收各向异性理论;实验测得了样品的光电流随外加偏压的非线性变化关系,实验中没有观察到光电流随外加偏压的增加而饱和的现象,进一步证明了GaAs样品中产生了倍频吸收.     

High-purity semi-insulating 4H-SiC for microwave device applications

High-purity, semi-insulating (HPSI) 4H-SiC crystals with diameters up to 75 mm have been grown by the seeded sublimation technique without the intentional introduction of elemental deep-level dopants, such as vanadium. Wafers cut from these crystals exhibit homogeneous activation energies near mid gap and thermally stable semi-insulating (SI) behavior (>10⁹ ohm-cm) throughout device processing. Secondary ion mass spectroscopy, deep-level transient spectroscopy, optical admittance spectroscopy, and electron paramagnetic resonance data suggest that the SI behavior originates from several deep levels associated with intrinsic point defects. Micropipe densities in HPSI substrates have been demonstrated to be as low as 10 cm⁻² in 2-in. substrates, and the room-temperature thermal conductivity of this material is near the theoretical maximum of 5 W/cm·K for 4H-SiC. Devices fabricated on these HPSI wafers do not exhibit any substrate related back-gating effects and have power densities as high as 5.2 W/mm with 63% power added efficiency.     

Photoluminescence of electron-hole plasma in semi-insulating undoped GaAs

The dependence of the photoluminescence spectrum of electron-hole plasma in semi-insulating undoped GaAs on the concentration of the background carbon impurity N_C(3×10¹⁵ cm^?3≤N_C≤4×10¹⁶ cm^?3) is studied at 77 K. It is established that the density of the electron-hole plasma, which is equal to n _e?h ≈1.1×10¹⁶ cm^?3 in crystals with the lowest impurity concentration at an excitation intensity of 6×10²² photons/(cm² s), decreases considerably as the value of N_C increases in the range mentioned above. A decrease in the density of the electron-hole plasma with increasing N_C is attributed to the effect of fluctuations in the carbon concentration N_C, which give rise to a nonuniform distribution of interacting charge carriers and to localization of holes in the tails of the density of states of the valence band.     

Role of deep-level centers in compensated semi-insulating GaAs

Requirements are defined for GaAs materials intended for solid-state detectors of ionizing radiation. A model is proposed to ascertain the role of deep-level centers in compensated semi-insulating GaAs. The model consists of transport equations and a charge-balance equation describing carrier transitions in a multi-level system. Its numerical analysis is performed to ascertain the relationship to be satisfied by dopant concentrations.     

Novel metal-semiconductor-metal photodetectors on bulk semi-insulating indium phosphide

Depositing Pd or An on InP at substrate temperatures near 77 K (LT) has previously been found to significantly reduce the interaction between the metal and semiconductor upon formation of the interface. In this letter, this technique was used to fabricate metal-semiconductor-metal photodetectors (MSMPDs) on semi-insulating (SI) InP substrates with superior characteristics compared to detectors formed using standard room temperature (RT) metal deposition. Detectors having a LT-Ps-SI-InP structure had a dark current of 80 nA at 5 V, which was a factor of 4 lower than the dark current of conventional MSMPDs. Additionally, LT-Pd-SI-InP MSMPDs exhibited excellent saturation characteristics and a responsivity of 0.75 A/W. Detectors with an indium-tin-oxide (ITO)-LT-Au (200 /spl Aring/)-SI-InP structure had a higher responsivity of 1.0 A/W, due to the relative transparency of this metallization. In contrast, MSMPDs with RT metallizations had poor saturation characteristics, consistent with the results of others. The difference in the illuminated characteristics of MSMPDs with RT and LT metallizations was due to a change in the internal photoconductive gain mechanism. In RT detectors, hole trapping at interface states near the cathode dominated the gain mechanism. In LT detectors, the difference in carrier transit-times dominated.