GaN p–n junction diode formed by Si ion implantation into p-GaN

²⁸Si⁺ implantation into Mg-doped GaN, followed by thermal annealing in N₂ was performed to achieve n⁺-GaN layers. The carrier concentrations of the films changed from 3×10¹⁷ (p-type) to 5×10¹⁹ cm⁻³ (n-type) when the Si-implanted p-type GaN was properly annealed. Specific contact resistance (ρ_c) of Ti/Al/Pt/Au Ohmic contact to n-GaN, formed by ²⁸Si⁺ implantation into p-type GaN, was also evaluated by transmission line model. It was found that we could achieve a ρ_c value as low as 1.5×10⁻⁶ Ω cm² when the metal contact was alloyed in N₂ ambience at 600 °C. Si-implanted GaN p–n junction light-emitting diodes were also fabricated. Electroluminescence measurements showed that two emission peaks at around 385 and 420 nm were observed, which could be attributed to the near band-edge transition and donor-to-acceptor transition, respectively.     

Low-noise back-illuminated AlxGa1-xN-basedp-i-n solar-blind ultraviolet photodetectors

We report the growth, fabrication and characterization of Al_0.4Ga_0.6N-Al_0.6Ga_0.4N back-illuminated, solar-blind p-i-n photodiodes. The peak responsivity of the photodiodes is 27 and 79 mA/W at λ≈280 nm for bias voltages of 0 V and -60 V, respectively, with a UV-to-visible rejection ratio of more than three decades (at 400 nm). These devices exhibit very low dark current densities (~5 nA/cm² at -10 V). At low frequencies, the noise exhibits a 1/f-type behavior. The noise power density is S₀≈5×10^-25 A²/Hz at -12.7 V and the detectivity (D*) at 0 V is estimated to be in the range of 4×10¹¹-5×10¹³ cm·Hz^1/2 /W. Time-domain pulse response measurements in a front-illumination configuration indicate that the devices are RC-time limited and show a strong spatial dependence with respect to the position of the incident excitation, which is mainly due to the high resistivity of the p-type Al_0.4Ga_0.6 N layer     

Estimation for the capture cross-sections of surface state on p-Si surface by photovoltaic method

A new method which can nondestructively measure the surface-state density (SSD) D_s and estimate the capture cross-sections (CCS) of surface state σ⁰_n and σ⁻_p on surface of p-type semiconductor crystals is proposed. This method is based on the photovoltage measurements at various temperatures. The photovoltage experiment was carried out with a (1 1 1) p-type Si single crystal (N_A=4.8×10¹⁴ cm ⁻³). Owing to that the surface barrier height φ_BP=0.6421 V and the surface-recombination velocity s_n=9.6×10³ cm s⁻¹ of this sample can be determined, the SSD D_s=1.2×10¹¹ cm⁻² eV⁻¹ can therefore be obtained, furthermore CCS σ⁰_n≈5×10⁻¹⁴ cm² and σ⁻_p≈2×10⁻¹⁰ cm² can also be estimated. These results are consistent with that of related reports obtained by other methods.     

N掺杂MgZnO薄膜的p型导电稳定性研究

利用磁控溅射技术,以Mg0.06Zn0.94O为陶瓷靶材,制备了N掺杂p型Mg0.1 3Zn0.8 7O薄膜,薄膜的电阻率为42.45Ω·cm,载流子浓度为3.70×1017/cm3,迁移率为0.40cm2·V-1·s-1。研究了该薄膜p型导电性质在室温空气下随时间的变化情况。实验结果表明,薄膜的电阻率逐渐升高,载流子浓度降低,五个月以后,薄膜转变为n型导电,电阻率为85.58Ω·cm,载流子浓度为4.53×1016/cm3,迁移率为1.61cm2·V-1·s-1。真空热退火后重新转变为p型。结果显示,其p型导电类型的转变与在空气中吸附H2O或H2等形成浅施主有关。     

High peak tunnel current densityGa0.47In0.53As Esaki diodes

High peak current density Ga_0.47In_0.53As interband tunnel diodes were fabricated by metal organic molecular beam epitaxy. A room temperature peak-to-valley current ratio of 16 and a peak tunnel current density of 9.2 kA/cm² were obtained in diodes doped to ~3×10¹⁹cm³ on both n-type and p-type sides. A peak-to-valley current ratio of 3.8, and a peak tunnel current density of 93.2 kA/cm² were obtained in diodes doped to ~10²⁰ cm^-3 on both n-type and p-type sides     

Measurements of residual defects and 1/f noise in ion-implanted p-channel MOSFET's

This paper describes the measurements of excess noise and residual defects of extremely low concentrations (<1 × 10⁹cm^-2) in ion-implanted p-channel MOSFET's. The activation energy and the density of the residual defects after high-temperature annealing were measured using a transient capacitance technique. The test FET's were ion-implanted with fluences of 5 × 10¹¹to 4 × 10¹²using³¹p⁺,¹¹B⁺, or²⁸Si⁺species. A post-implant anneal was carried out in an N2or an Ar ambient for 20 min at various temperatures. For¹¹B⁺-implanted MOSFET's after annealing above 1000°C, a high residual defect concentration was observed near the conduction band edge; whereas after annealing the defect density as a result of²⁸Si⁺or³¹p⁺implantation was equal to that of control MOSFET's. The density-of-state data agree with the equilibrium measurements of excess (1/f) noise power. The excess noise was measured as a function of the drain current. The distribution of1/fnoise power versus potential minimum of holes in the equilibrium condition is similar to that of interface state density. In nonequilibrium operation, a reduction of excess noise was achieved owing to the presence of buried channel created by ion implant.     

P-type 4H and 6H-SiC high-voltage Schottky barrier diodes

High-voltage Schottky barrier diodes have been successfully fabricated for the first time on p-type 4H- and 6H-SiC using Ti as the barrier metal. Good rectification was confirmed at temperatures as high as 250°C. The barrier heights were estimated to be 1.8-2.0 eV for 6H-SiC and 1.1-1.5 eV for 4H-SiC at room temperature using both I-V and C-V measurements. The specific on resistance (R_on,sp) for 4H- and 6H-SiC were found to be 25 mΩ cm^-2 and 70 mΩ cm^-2 at room temperature. A monotonic decrease in resistance occurs with increasing temperature for both polytypes due to increased ionization of dopants. An analytical model is presented to explain the decrease of R_on,sp with temperature for both 4H and 6H-SiC which fits the experimental data. Critical electric field strength for breakdown was extracted for the first time in both p-type 4H and 6H-SiC using the breakdown voltage and was found to be 2.9×10⁶ V/cm and 3.3×10⁶ V/cm, respectively. The breakdown voltage remained fairly constant with temperature for 4H-SiC while it was found to decrease with temperature for 6H-SiC     

Evaluation of the potential of ZnSe and Zn(Mg)BeSe compounds forultraviolet photodetection

We report on blue-violet and ultraviolet (UV) light detectors based on ZnSe and Zn(Mg)BeSe compounds lattice matched onto GaAs substrates. Three types, namely p-i-n, Schottky, and metal-semiconductor-metal (MSM) structures, have been fabricated. A comprehensive characterization of the spectral response is developed in each case. Performances, specifications, and advantages of each kind of device are detailed, p-i-n ZnBeSe-ZnMgBeSe photodiodes exhibit a high responsivity (0.17 A/W at 150 nm) and a high rejection rate (10⁴ ). Losses by recombination in the top p-type layer and p-type doping limitations lead to a decrease of the high energy response which is their major drawback. Thanks to the position of their depleted region on top of the structure. Schottky barriers and MSM photodetectors are much more suited for UV detection. With Schottky diodes, high efficiencies are obtained over the whole UV-A and -B ranges. Detectivity values above 10¹¹ mHz^1/2 W^-1 have been measured. MSM detectors appear as an attractive alternative to Schottky barrier diodes with as high a response and nearly as low noise levels. This study thus demonstrates the potential of ZnSe- and ZnMgBeSe-based Schottky barriers and MSM devices for efficient detection in the UV region     

Noise performance of InGaAs-InP quantum-well infraredphotodetectors

Dark current noise measurements were carried out between 10 and 10 ⁴ Hz at T=80 K on two InGaAs-InP quantum-well infrared photodetectors (QWIPs) designed for 8-μm infrared (IR) detection. Using the measured noise data, we have calculated the thermal generation rate, bias-dependant gain, electron trapping probability, and electron diffusion length. The calculated thermal generation rate (~7×10 ²² cm^-3·s^-1) is similar to AlGaAs-GaAs QWIPs with similar peak wavelengths, but the gain is 50× larger, indicating improved transport and carrier lifetime are obtained in the binary InP barriers     

Dual-type CMOS gate electrodes by dopant diffusion from silicide

Dual work function gate electrodes have been implemented in a 1-μm CMOS process. Dopant atoms were implanted into tungsten silicide simultaneously with the source-drain implantations and subsequently diffused into the underlying polycrystalline silicon layer by rapid thermal annealing. Physical analyses showed that arsenic and boron could easily be incorporated in the polysilicon to concentrations greater than 10²⁰ cm^-3. Capacitor and transistor measurements confirmed that n⁺ and p⁺ silicon could be obtained, with a difference of about 1 V between the respective flat-band voltages. By comparison with conventional n-type gate MOSFETs, it was verified that significantly improved subthreshold characteristics were obtained with p-type PMOS gate electrodes     

Formation of 0.05-μm p+-n and n+-pjunctions by very low (<500 eV) ion implantation

The current-voltage (I-V) characteristics of ultrashallow p⁺ -n and n⁺-p diodes, obtained using very-low-energy (<500-eV) implantation of B and As, are presented. the p⁺-n junctions were formed by implanting B⁺ ions into n-type Si (100) at 200 eV and at a dose of 6×10¹⁴ cm^-2, and n⁺-p junctions were obtained by implanting As⁺ ions into p-type (100) Si at 500 eV and at a dose 4×10¹² cm^-2. A rapid thermal annealing (RTA) of 800°C/10 s was performed before I-V measurements. Using secondary ion mass spectrometry (SIMS) on samples in-situ capped with a 20-nm ²⁸Si isotopic layer grown by a low-energy (40 eV) ion-beam deposition (IBD) technique, the depth profiles of these junctions were estimated to be 40 and 20 nm for p⁺-n and n⁺-p junctions, respectively. These are the shallowest junctions reported in the literature. The results show that these diodes exhibit excellent I-V characteristics, with ideality factor of 1.1 and a reverse bias leakage current at -6 V of 8×10^-12 and 2×10^-11 A for p⁺-n and n⁺-p diodes, respectively, using a junction area of 1.96×10^-3 cm²     

In-situ low energy BF2+ion doping for silicon molecular beam epitaxy

An experimental study of the p-type ion dopant BF2+ in silicon molecular beam epitaxy (MBE) is described. BF2+ was used to dope MBE layers during growth to levels ranging from 1 × 10¹⁶/cm³to 4 × 10¹⁸/cm³over a growth temperature range of 650°C to 1000°C. The layers were evaluated using spreading resistance, chemical etching, and secondary ion mass spectroscopy. Complete dopant activation was observed for all growth temperatures. Remnant fluorine in the epitaxial layer was less than 2 × 10¹⁶/cm³in all cases. Diffused p-n junction diodes fabricated in BF2+-doped epitaxial material showed hard reverse breakdown characteristics.     

Study of the Drain Leakage Current in Bottom-Gated Nanocrystalline Silicon Thin-Film Transistors by Conduction and Low-Frequency Noise Measurements

The drain leakage current in n-channel bottom-gated nanocrystalline silicon (nc-Si) thin-film transistors is investigated systematically by conduction and low-frequency noise measurements. The presented results indicate that the leakage current, controlled by the reverse biased drain junction, is due to Poole-Frenkel emission at low electric fields and band-to-band tunneling at large electric fields. The leakage current is correlated with single-energy traps and deep grain boundary trap levels with a uniform energy distribution in the band gap of the nc-Si. Analysis of the leakage current noise spectra indicates that the grain boundary trap density of 8.5 times 10¹² cm ^-2 in the upper part of the nc-Si film is reduced to 2.1 times 10¹² cm^-2 in the lower part of the film, which is attributed to a contamination of the nc-Si bulk by oxygen     

Au/Pt/Ti/Ni ohmic contacts to p-ZnTe

Ohmic contacts of Au/Pd/Ti/Ni to p-ZnTe show a minimum specific contact resistance of 10^-6 Ωcm² for a p-type doping level of 3×10¹⁹ cm^-3 and at an annealing temperature of 300°C. The Ni and Ti layers are very effective in improving the electrical properties of these contact     

Properties of ion-implanted junctions in mercury—cadmium—telluride

The formation of n-p junctions by ion-implantation in Hg0.71Cd0.29Te is shown to be a result of implantation damage. n-p photodiodes have been made by implantation of Ar, B, Al, and P in a p-type substrate with acceptor concentration of 4 × 10¹⁶cm^-3. The implanted n-type layer is characterized by sheet electron concentration of 10¹⁴to 10¹⁵cm^-2and electron mobility higher than 10³cm². V^-1. s^-1, for ion doses in the range 10¹³-5 × 10¹⁴cm^-2. The photodiodes have a spectral cutoff of 5.2 µm, quantum efficiency higher than 80 percent, and differential resistance by area product above 2000 Ω . cm²at 77 K. The temperature dependence of the differential resistance is discussed. The junction capacitance dependence on reverse voltage fits a linearly graded junction model. Reverse current characteristics at 77 K have been investigated using gate-controlled diodes. The results suggest that reverse breakdown is dominated by interband tunneling in field-induced junctions at the surface, for both polarities of surface potential.     

Generation-recombination noise in GaN/AlGaN heterostructure fieldeffect transistors

Local levels with a large activation energy E_a~0.8-1.0 eV have been observed in low-frequency noise measurements of GaN/AlGaN heterostructure field effect transistors (HFETs and MOS-HFETs) grown on 4N-SiC substrates. The noise might come from the thin (30 nm) AlGaN barrier layer. The estimates of the level parameters based on this assumption resulted in reasonable values of capture cross section σ_n≈(10^-12-10^-13) cm² and trap concentration N_t≈5-10¹⁶ cm^-3     

Modeling the variation of the low-frequency noise in polysiliconemitter bipolar junction transistors

The variation of the low-frequency noise in polysilicon emitter bipolar junction transistors (BJTs) was investigated as a function of emitter area (A_E). For individual BJTs with submicron-sized A _E, the low-frequency noise strongly deviated from a 1/f-dependence. The averaged noise varied as 1/f, with a magnitude proportional to A_E^-1, while the variation in the noise level was found to vary as A_E^-1.5. A new expression that takes into account this deviation is proposed for SPICE modeling of the low-frequency noise. The traps responsible for the noise were located at the thin SiO₂ interface between the polysilicon and monosilicon emitter. The traps' energy level, areal concentration and capture cross-section were estimated to 0.31 eV, 6×10⁸ cm^-2 and 2×10^-19 cm ², respectively     

Molecular beam epitaxial GaAs/AlGaAs heterojunction bipolartransistors on (311)A GaAs substrates with all-silicon doping

The authors have investigated the characteristics and reproducibility of Si-doped p-type (311)A GaAs layers for application to heterojunction bipolar transistors (HBTs) grown by molecular beam epitaxy (MBE). The authors obtained p=2.2×10¹⁹ cm^-3 in a layer grown at 670°C. They have used all-Si doping to grow n-p-n transistors. These devices exhibit excellent DC characteristics with β=230 in a device with base doping of p=4×10¹⁸ cm^-3     

Demonstration of an SiC neutron detector for high-radiationenvironments

Neutron response studies have been performed on Schottky diodes fabricated using 4H-SiC material. These studies indicate that neutron detection using SiC diodes is possible without significant degradation in the energy resolution, noise characteristics or, most importantly, the neutron counting rate even after exposure to neutron fluences of 3.4×10¹⁷ n_th/cm² (1×10¹⁷ n_fast/cm²; E_n.fast >1 MeV), the highest yet examined. The results represent orders of magnitude increased device lifetime in neutron fields compared to commercial silicon based detectors. Additionally, detector response was found to be linear up to thermal neutron fluxes of 2000 n_th/cm²/s. However, degradation in the charge collection efficiency due to neutron damage-induced defects prevented self-biased operation after exposures above ~5.7×10¹⁶ n _th/cm². A carrier removal rate of 9.7±0.7 cm^-1 was calculated from C-V doping profile measurements on neutron irradiated samples. These results demonstrate the viability of SiC-based detectors for a variety of radiation monitoring applications     

Si/Si1-xGex heterojunction bipolartransistors produced by limited reaction processing

Si/Si_1-xGe_x heterojunction transistors (HBTs) fabricated by a chemical vapor deposition (CVD) technique are reported. A rapid thermal CVD limited-reaction processing (LRP) technique was used for the in situ growth of all three device layers, including a 20-mm Si_1-xGe_x layer in the base. The highest current gains observed (β=400) were for a Si/Si_1-x Ge_x HBT with a base doping of 7×10¹⁸ cm^-3 near the junction and a shallow arsenic implant to form ohmic contacts and increase current gain. Ideal base currents were observed for over six decades of current and the collector current remained ideal for nearly nine current decades starting at 1 pA. The bandgap difference between a p-type Si layer doped to 5×10¹⁷ cm^-3 and the Si_1-xGe_x(x=0.31) base measured 0.27 eV. This value was deduced from the measurements of the temperature dependence of the base current and is in good agreement with published calculations for strained Si_1-xGe_x layers on Si