Diamond thin-film recessed gate field-effect transistors fabricatedby electron cyclotron resonance plasma etching

A new technique for etching boron-doped homoepitaxial diamond films was used to fabricate mesa-isolated recessed gate field-effect transistors that operate at temperatures up to 350°C. The upper temperature range is limited by the gate leakage current. The room-temperature hole concentration and mobility of the diamond film active layer were 1.2×10¹³ cm^-3 and 280 cm ²/V-s, respectively. The maximum transconductance was 87 μS/mm at 200°C     

Electron and hole traps in SiO2 films thermally grown onSi substrates in ultra-dry oxygen

The densities of electron and hole traps in SiO₂ films, thermally grown on Si substrates in ultra-dry oxygen, were compared with those in SiO₂ films grown in pyrogenic steam (wet-oxide films). The results show that ultra-dry-oxide films have an undetectable density of electron traps that is less that 10¹¹/cm² , and little interface-states generation during carrier injection. However, hole traps in ultra-dry-oxide films are high, (2.6±0.1)×10¹²/cm² compared with (1.3±0.2)×10¹²/cm² in wet-oxide films, and these increase by a factor of two with post-oxidation anneal in ultra-dry Ar. The results of electron spin resonance measurements of E' centers in SiO₂ films are consistent with the results of electrical measurements. These suggest that there is a tradeoff correlation between the density of electron traps and hole traps, with respect to the amount of water- or hydrogen-related defects in SiO₂     

Bulk and surface properties of amorphous hydrogenated fluorinatedsilicon grown from SiF4 and H2

A detailed study of the growth of amorphous hydrogenated fluorinated silicon (a-Si:H, F) from a DC glow discharge in SiF₄ and H₂ is discussed. The electrical properties of the films can be varied over a very wide range. The bulk properties of the best films that were measured included an Urbach energy E_u =43 meV, a deep-level defect density N_s=1.5×10¹⁵ cm^-3, and a hole drift mobility of 8×10^-3 cm² V^-1 s^-1, which reflects a characteristic valence band energy of 36 meV. It was found that E_u, N _s, and the density of surface states N_ss are related to each other. Under the deposition condition of the films with the best bulk properties, N_ss reaches its highest value of 1×10¹⁴ cm^-2. It is suggested that in growth from SiF₄/H₂, the density of dangling bonds at the growing surface is very sensitive to the deposition conditions     

Ohmic contacts on diamond by B ion implantation and Ti-Aumetallization

Low-resistance ohmic contacts have been fabricated on a natural IIb semiconducting diamond crystal and on undoped polycrystalline diamond films by B ion implantation and subsequent metallization with a Ti-Au bilayer metallization. A high B concentration of ~7×10²⁰ cm^-3 at the surface was obtained by ion implantation, a post-implant anneal, and a subsequent chemical removal of the graphite layer that resulted from the radiation damage. A bilayer metallization of Ti followed by Au annealed at 850°C yielded a specific contact resistance value on the order of 10^-6 Ω-cm² for chemical-vapor-deposition-grown polycrystalline films and on the order of 10^-5 Ω-cm² for the semiconducting natural crystal     

High Tg hole transport polymers for the fabrication ofbright and efficient organic light-emitting devices with an air-stablecathode

An organic electroluminescent device with a luminous efficiency of 20 Im/W, at 14 cd/m², and an external quantum efficiency of 4.6% has been fabricated using a high T_g hole transport polymer, a small molecule emission layer, and a LiF/Al cathode. The device quantum efficiency can be increased by tuning the ionization potential of the hole-transport moieties. When tested under pulsed voltage mode, in air at room temperature, and without any encapsulation, the device showed a high peak brightness of 4.4×10⁶ cd/m² at 100 A/cm² and an efficiency of 4.4 cd/A     

⟨110⟩-oriented GaAs MESFETs

GaAs metal semiconductor field-effect transistors (MESFETs) have been successfully fabricated on molecular-beam epitaxial (MBE) films grown on the off-axis (110) GaAs substrate. The (110) substrates were tilted 6° toward the (111) Ga face in order to produce device quality two-dimensional MBE growth. Following the growth of a 0.4-μm undoped GaAs buffer, a 0.18-μm GaAs channel with a doping density of 3.4×10¹⁷ cm^-3 and a 0.12-μm contact layer with a doping density of 2×10¹⁸ cm^-3, both doped with Si, were grown. MESFET devices fabricated on this material show very low-gate leakage current, low output conductance, and an extrinsic transconductance of 200 mS/mm. A unity-current-gain cutoff frequency of 23 GHz and a maximum frequency of oscillation of 56 GHz have been achieved. These (110) GaAs MESFETs have demonstrated their potential for high-speed digital circuits as well as microwave power FET applications     

Optimization of the germanium preamorphization conditions forshallow-junction formation

Shallow p⁺-n and n⁺-p junctions were formed in germanium preamorphized Si substrates. Germanium implantation was carried out over the energy range of 50-125 keV and at doses from 3×10¹⁴ to 1×10¹⁵ cm^-2. p ⁺-n junctions were formed by 10-keV boron implantation at a dose of 1×10¹⁵ cm^-2. Arsenic was implanted at 50 keV at a dose of 5×10¹⁵ cm^-2 to form the n⁺-p junctions. Rapid thermal annealing was used for dopant activation and damage removal. Ge, B, and As distribution profiles were measured by secondary ion mass spectroscopy. Rutherford backscattering spectrometry was used to study the dependence of the amorphous layer formation on the energy and dose of germanium ion implantation. Cross-sectional transmission electron microscopy was used to study the residual defects formed due to preamorphization. Complete elimination of the residual end-of-range damage was achieved in samples preamorphized by 50-keV/1×10¹⁵ cm^-2 germanium implantation. Areal and peripheral leakage current densities of the junctions were studied as a function of germanium implantation parameters. The results show that high-quality p⁺-n and n⁺-p junctions can be formed in germanium preamorphized substrates if the preamorphization conditions are optimized     

High quality SiO2/Si interfaces of poly-crystallinesilicon thin film transistors by annealing in wet atmosphere

A new post-metallization annealing technique was developed to improve the quality of metal-oxide-semiconductor (MOS) devices using SiO ₂ films formed by a parallel-plate remote plasma chemical vapor deposition as gate insulators. The quality of the interface between SiO₂ and crystalline Si was investigated by capacitance-voltage (C-V) measurements. An H₂O vapor annealing at 270°C for 30 min efficiently decreased the interface trap density to 2.0×10¹⁰ cm^-2 eV^-1, and the effective oxide charge density from 1×10 ¹² to 5×10⁹ cm^-2. This annealing process was also applied to the fabrication of Al-gate polycrystalline silicon thin film transistors (poly-Si TFT's) at 270°C. In p-channel poly-Si TFT's, the carrier mobility increased from 60-400 cm² V^-1 s^-1 and the threshold voltage decreased from -5.5 to -1.7 V     

Role of dopant incorporation in low-temperature Si epitaxial growthby rapid thermal processing chemical vapor deposition

The authors have demonstrated that epitaxial growth temperatures can be lowered by dopant incorporation using rapid thermal processing chemical vapor deposition. Heavily As- and B-doped epitaxial layers with very abrupt dopant transition profiles and relatively uniform carrier distributions have been grown at 800°C. The film quality and defect formation were strongly dependent on the electrically active dopant concentration. The defect density as a function of electron concentration shows a sharp transition at 3×10¹⁸ cm^-3 for As-doped epitaxy. For B-doped epitaxy, the film quality was monocrystalline with smooth surface morphology for hole concentrations above 5×10¹⁹ cm^-3     

GaAs/AlGaAs heterojunction Pnp bipolar transistors grownon (100) Si by molecular beam epitaxy

GaAs/AlGaAs Pnp heterojunction bipolar transistors (HBTs) were fabricated and tested on (100) Si substrates for the first time. A common-emitter current gain of β=8 was measured for the typical devices with an emitter area of 50×50 μm² at a collector current density of 1×10⁴ A/cm² with no output negative differential resistance up to 280 mA, highest current used. A very high base-collector breakdown voltage of 10 V was obtained. Comparing the similar structures grown on GaAs substrates, the measured characteristics clearly demonstrate that device grade hole injection can be obtained in GaAs on Si epitaxial layers despite the presence of dislocations     

GaAs bipolar transistors with a Ga0.5In0.5Phole barrier layer and carbon-doped base grown by MOVPE

GaAs bipolar transistors with a 50-Å-thick lattice matched Ga_0.5In_0.5P layer between the emitter and base acting as a hole repelling potential barrier in the valence band were fabricated from films grown by metalorganic vapor phase epitaxy (MOVPE). The 1000-Å-thick base was doped with carbon to 2×10¹⁹ cm^-3, resulting in a base sheet resistance of 250 Ω/□. Carbon has been chosen because of its low diffusivity. Using the barrier layer as an etch stop the authors fabricated mesa-type broad-area devices. The output characteristics of the devices are ideal with very small offset voltages and infinite Early voltages. Common emitter current gains of up to 70 at 10⁴ A/cm² collector current density were obtained. The current gain is clearly higher than the one calculated for a bipolar junction transistor with the same doping profile because the base-emitter hole current is suppressed by the Ga_0.5In_0.5P potential barrier in the valence band     

KrF excimer laser annealed TFT with very high field-effect mobilityof 329 cm2/V-s

A thin-film transistor (TFT) with a maximum field-effect mobility of 320 cm²/V-s, an on/off current ratio of 7.6×10⁷ , a threshold voltage of 6.7 V and a subthreshold slope of 0.37 V/decade was fabricated by using pulse laser annealing processes. Amorphous silicon films (a-Si:H) with a very low impurity concentration of 4×10¹⁸ cm^-3 for oxygen, 1.5×10¹⁸ cm^-3 for carbon, and 2×10¹⁷ cm^-3 for nitrogen were deposited by a plasma chemical vapor deposition (CVD) method and annealed by KrF excimer laser (wavelength of 248 nm). The Raman spectroscopy technique was a useful tool for optimizing laser annealing conditions. Experimental results show that two factors are very important for fabricating very-high mobility TFTs: (1) utilizing high-purity as-deposited a-Si:H film; and (2) performing whole laser annealing processes sequentially in a vacuum container and optimizing illumination conditions     

Enhancement mode InP MISFET's with sulfide passivation andphoto-CVD grown P3N5 gate insulators

High performance enhancement mode InP MISFET's have been successfully fabricated by using the sulfide passivation for lower interface states and with photo-CVD grown P₃N₅ film used as gate insulator. The MISFET's thus fabricated exhibited exhibited pinch-off behavior with essentially no hysteresis. Furthermore the device showed a superior stability of drain current. Specifically under the gate bias of 2 V for 10⁴ seconds the room temperature drain current was shown to reduce from the initial value merely by 2.9% at the drain voltage of 4 V. The effective electron mobility and extrinsic transconductance are found to be about 2300 cm ²/V·s and 2.7 mS/mm, respectively. The capacitance-voltage characteristics of the sulfide passivated InP MIS diodes show little hysteresis and the minimum density of interface trap states as low as 2.6×10¹⁴/cm² eV has been attained     

High current p/p+-diamond Schottky diode

Epitaxial p-type Schottky diodes have been fabricated on p⁺ -substrate. While the activation energy of the epitaxial layer conductivity is 390 meV, that of the substrate is only 50 meV. At forward bias the substrate conductivity dominates above 150°C, leading for a 5×10^-5 cm² area contact to a series resistance of 14 Ω at 150°C reducing to 8 Ω at 500°C. To our knowledge, this is the lowest series resistance reported so far for a diamond Schottky diode enabling extremely high current densities of 10³ A/cm and a current rectification ratio at ±2 V of 10⁵ making these diodes already attractive as high temperature rectifiers     

Dynamic characterisation of Si/SiGe power HBTs

Si/SiGe power heterojunction bipolar transistors (HBTs) grown by MBE were dynamically characterised in the common-base configuration. At an emitter current density of 1.1×10⁵ A/cm², a maximum frequency of oscillation of 49 GHz was observed. At 10 GHz a maximum unilateral gain of 14 dB is available, and a CW output power of 1.3 W/mm for a device with 10 parallel emitter-fingers of 1×10 μm² each was predicted, from CW measurements     

Steady-state and transient forward current-voltage characteristicsof 4H-silicon carbide 5.5 kV diodes at high and superhigh currentdensities

Steady-state and transient forward current-voltage I-V characteristics have been measured in 5.5 kV p⁺-n-n⁺ 4H-SiC rectifier diodes up to a current density j≈5.5×10 ⁴ A/cm². The steady-state data are compared with calculations in the framework of a model, in which the emitter injection coefficient decreases with increasing current density. To compare correctly the experimental and theoretical results, the lifetime of minority carriers for high injection level, τ_ph, has been estimated from transient characteristics. At low injection level, the hole diffusion length L_pl has been measured by photoresponse technique. For a low-doped n-base, the hole diffusion lengths are L_pl≈2 μm and L_ph≈6-10 μm at low and high injection levels respectively. Hole lifetimes for low and high injection levels are τ_pl≈15 ns and τ_ph≈140-400 ns. The calculated and experimental results agree well within the wide range of current densities 10 A/cm ²3 A/cm². At j>5 kA/cm², the experimental values of residual voltage drop V is lower than the calculated ones. In the range of current densities 5×10³ A/cm²4 A/cm², the minimal value of differential resistance R_d =dV/dj is 1.5×10^-4 Ω cm². At j>25 kA/cm², R_d increases with increasing current density manifesting the contribution of other nonlinear mechanisms to the formation steady-state current-voltage characteristic. The possible role of Auger recombination is also discussed     

Reliability of AlInAs/GaInAs heterojunction bipolar transistors

The reliability of high-performance AlInAs/GaInAs heterojunction bipolar transistors (HBTs) grown by molecular beam epitaxy (MBE) is discussed. Devices with a base Be doping level of 5×10¹⁹ cm^-3 and a base thickness of approximately 50 nm displayed no sign of Be diffusion under applied bias. Excellent stability in DC current gain, device turn-on voltage, and base-emitter junction characteristics was observed. Accelerated life-test experiments were performed under an applied constant collector current density of 7×10⁴ A/cm² at ambient temperatures of 193, 208, and 328°C. Junction temperature and device thermal resistance were determined experimentally. Degradation of the base-collector junction was used as failure criterion to project a mean time to failure in excess of 10⁷ h at 125°C junction temperature with an associated activation energy of 1.92 eV     

High performance poly-Si TFTs fabricated using pulsed laserannealing and remote plasma CVD with low temperature processing

Key technologies for fabricating polycrystalline silicon thin film transistors (poly-Si TFTs) at a low temperature are discussed. Hydrogenated amorphous silicon films were crystallized by irradiation of a 30 ns-pulsed XeCl excimer laser. Crystalline grains were smaller than 100 nm. The density of localized trap states in poly-Si films was reduced to 4×10¹⁶ cm^-3 by plasma hydrogenation only for 30 seconds. Remote plasma chemical vapor deposition (CVD) using mesh electrodes realized a good interface of SiO ₂/Si with the interface trap density of 2.0×10¹⁰ cm^-2 eV^-1 at 270°C. Poly-Si TFTs were fabricated at 270°C using laser crystallization, plasma hydrogenation and remote plasma CVD. The carrier mobility was 640 cm²/Vs for n-channel TFTs and 400 cm²/Vs for p-channel TFTs. The threshold voltage was 0.8 V for n-channel TFTs and -1.5 V for p-channel TFTs. The leakage current of n-channel poly-Si TFTs was reduced from 2×10^-10 A/μm to 3×10^-13 A/μm at the gate voltage of -5 V using an offset gate electrode with an offset length of 1 μm     

Isolation on Si wafers by MeV proton bombardment for RF integratedcircuits

This paper studies issues related with using high energy protons to create local semi-insulating silicon regions on IC wafers for device isolation and realization of high-Q IC inductors. Topics on two approaches, i.e., one using Al as the radiation mask and the other using proton direct-write on wafers were studied. It was shown that Al can effectively mask the proton bombardment of 15 MeV up to the fluence of 10¹⁷ cm^-2. For the unmasking direct write of the proton bombardment, isolation in the silicon wafer can be achieved without damaging active devices if the proton fluence is kept below 1×10¹⁴ cm^-2 with the substrate resistivity level chosen at 140 Ω-cm, or kept at 1×10¹⁵ cm ^-2 with the substrate resistivity level chosen at 15 Ω-cm. Under the above approaches, the 1 h-200°C thermal treatment, which is necessary for device final packaging, still gives enough high resistivity for the semi-insulating regions while recovering somewhat the active device characteristics. For the integrated passive inductor fabricated on the surface of the silicon wafer, the proton radiation improves its Q value     

Device simulation of submicrometer gate p+-i-p+ diamond transistors

Two-dimensional device simulation of submicrometer gate diamond p ⁺-i-p⁺ transistors with a SiO₂ gate insulator was investigated using the MEDICI device simulation program. A large modulation of the source-to-drain current was obtained in the accumulation mode. The computed diamond device characteristics were equivalent or better than the simulation results of 6H-SiC MESFET's. It was concluded that the problems in diamond MESFET associated with the deep acceptor levels due to boron doping can be overcome in the p⁺ -i-p⁺ diamond FET's because of the hole injection and the space charge limited current