Electrical passivation by hydrogen plasma treatment of transition metal impurities in germanium

Transition metal impurities in germanium introduce deep levels in the band gap, which may influence the lifetime of carriers and leakage currents of devices. In this work it is shown that Ti, Cr and Fe centres in germanium can be passivated using plasma hydrogenation. The metals have been implanted at 90 keV in n- and p-type wafers and in-diffused during a 5 min thermal anneal at 500 °C. Samples have been hydrogenated using a DC plasma for 4 h at 200 °C and Schottky diodes were made for measurement using DLTS. It is found that the levels of metal impurities are passivated by hydrogenation. Characteristic hole and electron traps are assigned to the irradiation damage induced by the direct plasma exposure. Metal-specific levels are tentatively assigned to transition metal–hydrogen-related centres. Two hole traps at 0.05 and 0.10 eV above the valence band are only present in the Cr-doped samples and are tentatively assigned to chromium–hydrogen complexes. A comparison is made with copper–hydrogen in germanium.     

High-performance p-channel poly-Si TFT's using electron cyclotronresonance hydrogen plasma passivation

This letter presents a summary of the first detailed investigation of electron cyclotron resonance (ECR) hydrogen plasma exposure treatments of p-channel poly-Si thin film transistors (TFT's). It is shown that ECR hydrogenation can be much more efficient than RF hydrogenation. Poly-Si p-channel TFT's fabricated at low temperatures (⩽625°C) and passivated with the ECR hydrogenation treatment are shown to exhibit ON/OFF current ratios of 7.6×10⁷, subthreshold swings of 0.62 V/decade, threshold voltages of -4.6 V, and hole mobilities over 18 cm²/V.s     

Surface recombination and sulfide passivation of GaN

The surface recombination velocity in n-type heteroepitaxial GaN(0001) is shown to decrease dramatically when the surface is chemically treated with aqueous and alcoholic solutions of inorganic sulfides, such as ammonium or sodium sulfide (NH₄)₂S_x and Na₂S). The room-temperature excitonic photoluminescence (PL) intensity increases by a factor of four to six after treatment, and improvements persist for at least seven months in room air. Various other chemicals commonly used in device processing are investigated and shown to change the PL intensity by factors ranging from 0.7 to 2.5, buffered oxide etching being the most beneficial. Schottky barrier diodes using gold as the contact metal are fabricated using a sulfide treatment prior to evaporation. The barrier height from capacitance-voltage measurements is as high as 1.63 ± 0.07 V, the highest value ever achieved on n-GaN. This result is evidence that the effect of surface states on the Fermi level has been substantially reduced by the treatment.     

High-power polarization-engineered GaN/AlGaN/GaN HEMTs without surface passivation

In this paper, a high-power GaN/AlGaN/GaN high electron mobility transistor (HEMT) has been demonstrated. A thick cap layer has been used to screen surface states and reduce dispersion. A deep gate recess was used to achieve the desired transconductance. A thin SiO/sub 2/ layer was deposited on the drain side of the gate recess in order to reduce gate leakage current and improve breakdown voltage. No surface passivation layer was used. A breakdown voltage of 90 V was achieved. A record output power density of 12 W/mm with an associated power-added efficiency (PAE) of 40.5% was measured at 10 GHz. These results demonstrate the potential of the technique as a controllable and repeatable solution to decrease dispersion and produce power from GaN-based HEMTs without surface passivation.     

High dose-rate hydrogen passivation of polycrystalline silicon CMOSTFTs by plasma ion implantation

Plasma ion implantation (PII) hydrogenation is an efficient method for defect passivation in polycrystalline silicon (poly-Si) thin film transistors (TFTs). We have developed a process that can achieve saturation of device parameter improvement in 30 min, whereas conventional plasma hydrogenation takes approximately 4 h. Our model predicts that much shorter process times are possible. We have analyzed the gate oxide charging which occurs during the PII process and controlled it to the extent that processed devices are damage-free. The long-term reliability of PII hydrogenated devices is superior to that of conventional parallel-plate plasma hydrogenated devices     

Deep center passivation in 3C-SiC by hydrogen plasma with a grid for damage suppression

In order to passivate deep levels, hydrogen was introduced into 3C-SiC by a hydrogen plasma treatment. The effects of hydrogen were investigated by deep level transient spectroscopy (DLTS). DLTS results indicated that hydrogen passivates deep levels in the as-grown sample. However, the results also indicated that the plasma treatment simultaneously forms deep levels originated from damages in the surface region. In order to suppress the damages, we introduced a grid between the sample and the plasma source during the plasma treatment. DLTS results showed that the grid reduces the deep levels originated from the damages, retaining the hydrogen passivation effects. The defect concentration is less than 10¹⁴ cm⁻³ for the sample treated by the hydrogen plasma with the grid and subsequently annealed at 300 °C.     

On the nature of the defect passivation in polycrystalline silicon by hydrogen and oxygen plasma treatments

The effect of hydrogen and oxygen plasmas on the properties of polycrystalline silicon films and thin-film transistors are investigated. The results clearly demonstrate that an oxygen plasma does not passivate grain boundary defects. However, an oxygen plasma treatment at 300 K still improves the electrical properties of thin-film transistors.<>     

Rapid thermal hydrogen passivation of polysilicon MOSFETs

The effectiveness of rapid thermal annealing as a passivation technique using Si₃N₄ as a solid source of H is discussed. Polysilicon MOSFETs with an on/off ratio of 10⁷ can be obtained through rapid thermal hydrogen passivation, compared to an on/off ratio of 10⁶ after furnace passivation. The improvement of subthreshold slope, threshold voltage, and channel transconductance compared to unpassivated MOSFETs is greater for rapid thermal annealing (RTA) than for furnace passivation     

Effect of surface passivation of AlGaN/GaN heterostructurefield-effect transistor

The effect of SiN passivation of the surface of AlGaN/GaN transistors is reported. Current deep level transient spectroscopy (DLTS) measurements were performed on the device before and after the passivation by a SiN film. The DLTS spectra from these measurements showed the existence of the same electron trap on the surface of the device. The DLTS spectrum obtained from the measurement of the passivated device showed a significantly lower peak for this trap. The discrepancy in the DLTS peak amplitude is explained by the effect of the passivation on the surface traps and underlines the surface nature of the major defect noticed in the device     

High-performance poly-Si TFTs with ECR-plasma hydrogen passivation

High-performance thin-film transistors (TFTs) with electron-cyclotron resonance (ECR) plasma hydrogen passivation fabricated by the use of laser-recrystallized multiple-strip-structure poly-Si film are discussed. These TFTs have n-channel enhancement-mode characteristics with a large transconductance, a high switching ratio, and a threshold voltage as low as 0.4 v. The ECR-plasma hydrogen passivation of laser-recrystallized poly-Si, reduces the trap density of poly-Si and increases the carrier mobility thus, desirable TFT characteristics are obtained. This passivation increased the transconductance (g_m) of a TFT and decreased the leakage current between the source and the drain. As a result, a switching ratio as high as 2.5×10⁹ and very low leakage current of the order of 10¹⁴ A can be achieved by these high-performance TFTs     

Study of passivation defects by electroluminescence in AlGaN/GaN HEMTS on SiC

This paper presents a new method of passivation control by electroluminescence (EL) in 0.15 μm AlGaN/GaN HEMT. The electroluminescence signature in one finger HEMTs (W = 1 × 100 μm), and eight fingers ones (W = 8 × 125 μm), is modified by defects located at the passivation/semiconductor interface and is characterized by a light emission along the drain contact. This abnormal emission reveals some modification of the electric field distribution in the gate-drain space probably induced by traps located at the passivation/semiconductor interface. These traps contribute to the creation of a virtual gate in the gate-drain space.     

Al-enhanced PECVD SiNx induced hydrogen passivation in string ribbon silicon

The effectiveness of manufacturable gettering and passivation technologies is investigated for their ability to improve the quality of a promising Si photovoltaic material. The results of this study indicate that a lifetime enhancement of 30 μs is attained when a backside screen-printed aluminum layer and a thin film of SiN_x, applied by plasma-enhanced chemical vapor deposition (PECVD), are simultaneously annealed at 850°C in a lamp-heated belt furnace. Based on the results of this study, a model is proposed to describe the Al-enhanced SiN_x induced hydrogen defect passivation in String Ribbon silicon due to the simultaneous anneal. According to this model, three factors play an important role: i) the release of hydrogen from the SiN_x film into the substrate; ii) the retention of hydrogen at defect sites in silicon; and iii) the generation of vacancies at the Al−Si interface due to the alloying process which increases the incorporation of hydrogen and creates a chemical potential gradient which enhances the migration of hydrogen in the substrate. A PC1D device simulation indicates that screen-printed cell efficiencies approaching 16% can be achieved if the gettering and passivation treatments examined in this study are employed, the substrate thickness is reduced, and a high-quality surface passivation scheme is applied.     

Hydrogen sulfide plasma passivation of indium phosphide

The electrical properties of the SiO₂-InP interface are improved using in-situ H₂S plasma pretreatments as a reliable method of sulfidizing the InP surface prior to film deposition. High frequency (1 MHz) and quasi-static capitance-voltage measurements on metal-insulator-semiconductor structures show reduced interface trap densities. X-ray photoemission spectroscopy analysis indicates that prior to film deposition, sulfur is bonded to phosphorus at the surface; but after film deposition, very little sulfur remains. Spectroscopic ellipsometry measurements confirm that the interface does remain modified even after film deposition, and photoluminescence data show increased signal intensity for thin SiO₂ film on InP with H₂S pretreatments as compared to untreated samples.     

Photoluminescence of anti-modulation-doped GaAs/AlGaAs single quantum well structures exposed to hydrogen plasma

Techniques of low-temperature photoluminescence (PL), photoluminescence excitation, and photoreflectance were used to study the effect of hydrogen plasma treatment at 260°C on antimodulation Si-doped GaAs/AlGaAs heterostructures with near-surface single quantum wells (QWs) grown by molecular-beam epitaxy. It was found that, in the case of excitation below the AlGaAs band gap, exciton PL from the QW is quenched due to an increase in the electric field in the structure. The reason for this is that the passivation of surface states by hydrogen results in the Fermi level depinning from the midgap of the nominally undoped p-type GaAs cap layer, while shallow-level impurities present in the layers of the structure are not neutralized (their complexes with hydrogen dissociate under the influence of illumination and strong electric fields).     

Electrical and optical activation studies of Si-implanted GaN

Comprehensive and systematic electrical and optical activation studies of Si-implanted GaN were made as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1×10¹³ cm^?2 to 5×10¹⁵ cm^?2 at room temperature. The samples were proximity-cap annealed from 1050°C to 1350°C with a 500-Å-thick AlN cap in a nitrogen environment. The optimum anneal temperature for high dose implanted samples is approximately 1350°C, exhibiting nearly 100% electrical activation efficiency. For low dose (≤5×10¹⁴ cm^?2) samples, the electrical activation efficiencies continue to increase with an anneal temperature through 1350°C. Consistent with the electrical results, the photoluminescence (PL) measurements show excellent implantation damage recovery after annealing the samples at 1350°C for 20 sec, exhibiting a sharp neutral-donor-bound exciton peak along with a sharp donor-acceptor pair peak. The mobilities increase with anneal temperature, and the highest mobility obtained is 250 cm²/Vs. The results also indicate that the AlN cap protected the implanted GaN layer during high-temperature annealing without creating significant anneal-induced damage.     

Cleaning and passivation of the Si(100) surface by low temperature remote hydrogen plasma treatment for Si epitaxy

This paper presents the results of a study of the hydrogen-passivated Si(100) surface prepared by a remote hydrogen plasma treatment which serves the dual purpose of cleaning and passivating the Si(100) surface prior to low temperature Si epitaxy by Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD). The remote hydrogen plasma treatment was optimized for the purposes of cleaning and passivation, respectively. To achieve a clean, defect-free substrate surface, the remote hydrogen plasma process was first optimized using Transmission Electron Microscopy (TEM) and Auger Electron Spectroscopy (AES). For hydrogen passivation, the substrate temperature was varied from room temperature to 250° C in order to investigate the degree of passivation as a function of substrate temperature by examining the amount of oxygen readsorbed on the substrate surface after air exposure. Low temperature Si expitaxy was subsequently performed on the air-exposed substrates without further cleaning to evaluate the effectiveness of the hydrogen passivation. It was found that better Si surface passivation is achieved at lower substrate temperatures as evidenced by the fact that less oxygen is observed on the surface using AES and Secondary Ion Mass Spectroscopy (SIMS) analyses. The amount of readsorbed oxygen on the H-passivated Si surface after a two hour air exposure was found to be as low as 0.1 monolayer from SIMS analysis. Using Reflection High Energy Electron Diffraction (RHEED) analysis, different surface reconstructions ((3 × 1) and (1 × 1)) were observed for H-passivated Si surfaces passivated at various temperatures, which was correlated to the results of AES and SIMS analyses. Epitaxial growth of Si films at 305° C was achieved on the air-exposed Si substrates, indicating a chemically inert Si surface as a result of hydrogen passivation. A novel electron-beam-induced-oxygen-adsorptiom phenomena was observed on the Hpassivated Si surface. Scanning Auger Microscopy (SAM) analysis was performed to study the reaction kinetics as well as the nature of Si—H bonds on the H-passivated Si surface. Preliminary results show that there is a two-step mechanism involved, and oxygen adsorption on the H-passivated Si surface due to electron beam irradiation may be due to the formation of O-H groups rather than the creation of Si—O bonds.     

The effect of surface passivation on the microwave characteristicsof undoped AlGaN/GaN HEMTs

Surface passivation of undoped AlGaN/CaN HEMT's reduces or eliminates the surface effects responsible for limiting both the RF current and breakdown voltages of the devices. Power measurements on a 2×125×0.5 μm AlGaN/GaN sapphire based HEMT demonstrate an increase in 4 GHz saturated output power from 1.0 W/mm [36% peak power-added efficiency (PAE)] to 2.0 W/mm (46% peak PAE) with 15 V applied to the drain in each case. Breakdown measurement data show a 25% average increase in breakdown voltage for 0.5 μm gate length HEMT's on the same wafer. Finally, 4 GHz power sweep data for a 2×75×0.4 μm AlGaN/GaN HEMT on sapphire processed using the Si₃N₄ passivation layer produced 4.0 W/mm saturated output power at 41% PAE (25 V drain bias). This result represents the highest reported microwave power density for undoped sapphire substrated AlGaN/GaN HEMT's     

Formation and passivation of defects in heterostructures with strained GaAs/InGaAs quantum wells as a result of treatment in a hydrogen plasma

The effect of processing heterostructures with GaAs/InGaAs quantum wells in the hydrogen plasma of an rf glow discharge on the photoluminescence spectrum and capacitive photovoltage of these structures is investigated. It is shown that strained quantum-well heterolayers hinder the diffusion of hydrogen and defects into the bulk, which causes the spatial distributions of recombination-active and passivated hydrogenic defect-like complexes in heterostructures, and the processes that create them, to differ appreciably from the same processes in uniform layers. Fiz. Tekh. Poluprovodn. 32, 1089–1093 (September 1998)     

Electrical transport properties of single GaN and InN nanowires

The transport properties of single GaN and InN nanowires grown by thermal catalytic chemical vapor deposition were measured as a function of temperature, annealing condition (for GaN) and length/square of radius ratio (for InN). The as-grown GaN nanowires were insulating and exhibited n-type conductivity (n ≈ 2×10¹⁷ cm⁻³, mobility of 30 cm²/V s) after annealing at 700°C. A simple fabrication process for GaN nanowire field-effect transistors on Si substrates was employed to measure the temperature dependence of resistance. The transport was dominated by tunneling in these annealed nanowires. InN nanowires showed resistivity on the order of 4×10⁻⁴ Ω cm and the specific contact resistivity for unalloyed Pd/Ti/Pt/Au ohmic contacts was near 1.09×10⁻⁷ Ω cm². For In N nanowires with diameters <100 nm, the total resistance did not increase linearly with length/square of radius ratio but decreased exponentially, presumably due to more pronounced surface effect. The temperature dependence of resistance showed a positive temperature coefficient and a functional form characteristic of metallic conduction in the InN nanowires.     

A study on the transient effect due to hydrogen passivation in InGaP HBTs

The transient effect of InGaP heterojunction bipolar transistors is studied. The current gain increases with V/sub BE/ bias and becomes stable after several sweeps. The time to reach steady state depends on the collector current I/sub C/ and the ambient temperature. A new electrical method was introduced to calculate the passivation ratio, which is defined as the number of donor hydrogen (H/sup +/) atoms divided by the number of negatively charged carbon atoms (C/sup -/) in the heavily doped base layer. A passivation ratio of 69.98% obtained by this method agrees very well with that measured by secondary ion mass spectrometry of 69%.