SiH4 Flow Research Articles

Growth and performance of n++ GaN cap layer for HEMTs applications

Apart from providing high-quality ohmic contacts to III-N devices, n++ GaN cap layers can eliminate surface-related current collapse effects in high-electron-mobility transistors (HEMTs). Various metal-organic chemical vapor deposition conditions and n-type doping are tested in GaN growth on sapphire by using triethylgallium as a Ga precursor, replacing more conventional trimethylgallium. Consequently, despite relatively low temperature of the growth at 800 °C to facilitate InAlN barrier capping, optimized growth conditions and SiH4 flow provided free electron concentration of 7.2 × 1019 cm−3 and mobility of 103 cm2/Vs. Moreover, electron concentration in the range of 1020 cm−3 is demonstrated by using flow modulation epitaxy. On the other hand, as calibration growths indicated, excessive SiH4 flow alone can lead to high density of edge dislocations and surface undulations without enhancing free electron concentration. 6 nm (Si: 4.2 × 1019 cm−3) and 8 nm thick (Si: 7.2 × 1019 cm−3) n++ GaN cap is implemented in normally-off n++ GaN/InAlN/AlN/GaN HEMTs grown on Si, with a collapse-free performance for the latter case. By calculating energy band and free carrier concentration profiles of the heterostructures it is shown, that free electrons of a sufficiently thick and doped n++ GaN cap can shield the channel from the unstable surface potential.

High‐Quality Nonpolar a‐Plane AlGaN Film Grown on Si‐Doped AlN Template by Metal Organic Chemical Vapor Deposition

High crystalline quality and flat a‐plane aluminum gallium nitride (AlGaN) films are obtained on Si‐doped AlN templates with a moderate silane (SiH4) flow rate by metal‐organic chemical vapor deposition (MOCVD). The effects of the SiH4 flow rate on the surface morphology, crystalline quality, stress state, and optical property of a‐plane AlN templates and AlGaN films are comprehensively investigated. As the SiH4 flow rate increases from 0 to 7.0 nmol min−1, the full width at half maximum of X‐ray rocking curve values along [0001]/[1–100] directions for the AlGaN films are monotonically reduced to 1124/1143 arcsec. Meanwhile, the surface root mean square roughness value is decreased to 0.88 nm. These achievements are attributed to the suppression of the anisotropy degrees and in‐plane stress of AlN templates. In addition, an excess SiH4 flow rate leads to deteriorated surface morphologies and increased basal plane stacking fault (BPSF) densities for both AlN and AlGaN films. This work suggests that doping AlN layers with an appropriate SiH4 flow rate is a promising route to obtain high‐quality a‐plane AlGaN films for efficient nonpolar deep ultraviolet (DUV) devices.

Influence of the substrate conductivity type on the electroluminescence properties of PP+IN and PIN+N diodes based on amorphous silicon carbide (a-Si1-xCx:H) / crystalline silicon (c-Si) heterostructures

The study of the conduction and light emission mechanisms of PIN diodes based on amorphous silicon-carbide (a-Si1-xCx:H) thin film and crystalline silicon (c-Si) substrates is reported in this work. Using the same low-temperature process (200 °C), PP+IN and PIN+N structures were fabricated on p-type and n-type silicon (Si) substrates, respectively. The plasma enhanced chemical vapor deposition (PECVD) technique was employed for the active layers deposition where two different CH4/SiH4 flow rates ratios of 30 sccm/6 sccm and 30 sccm/1 sccm were used. All structures show red-orange light emission in forward bias (FB). The structures with the active layer deposited with a lower SiH4 flow rate, display light emission with a higher intensity at a lower voltage bias.In addition, we related the current-voltage measurements with different conduction models and the dominant charge transport mechanisms in the PIN structures were proposed. The highest Si content structures were related to Fowler-Nordheim (F-N) tunneling, because of its active layer with lower barrier height. On the other hand, the lowest Si content structures were associated with the Poole-Frenkel (P-F) emission, due to a higher density of defects in localized tail states. The results showed the same conduction and emission mechanisms for the PP+IN and PIN+N diodes with the same active layer, regardless of the conduction type of substrate, proving that it is feasible to use the same process for developing light emission devices on p-type and n-type Si substrates.

Tribology dependence on both structures of bulk a-C:H:Si films and transfer layer via adjustable Si content

Si doped hydrogenated amorphous carbon (a-C:H:Si) films were fabricated in mixed atmosphere of SiH4 and Ar by magnetron sputtering methods, with different SiH4 flow rates. The microstructures and tribological performances were measured by Atomic Force Microscopy (AFM), Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy and Tribo-tests. The results showed that the as-fabricated a-C:H:Si films exhibited good tribological performances with low friction and wear. The -OH termination which was deduced by SiO structure inside the a-C:H:Si film reacted with water molecules in atmosphere could passivate the film and counterpart surface, leading to the low friction of a-C:H:Si film. The wear rate increased with the increase of SiH4 gas flow rate, which could be attributed to the formation and increase of SiC phase with high hardness. The SiC phase enhanced the three-body abrasion between the contact surfaces, which increase the wear of the a-C:H:Si film at high SiH4 flow rate.

Modeling and simulation of coverage and film properties in deposition process on large-scale pattern using statistical ensemble method

This study modeled deposition processes using statistical ensemble and feature-scale voxel methods to predict the coverage and film properties on a large-scale pattern for the first time. Certain new concepts, such as the use of probabilities to express physical and chemical phenomena occurring on the surface, interaction among voxels, and super particles for fast calculations, were introduced. Further, the model was used to analyze the experimental characteristic variation between the morphology and film density of SiN in low-temperature plasma-enhanced chemical vapor deposition using a SiH4/NH3/N2 gas mixture with different SiH4 flow rates, which has not been found in SiO2 films. The simulation results demonstrated the effect of the precursor mass in the gas phase on surface migration and morphology formation. In addition, a short residence time was required to prevent the generation of large and heavy precursors to realize good SiN coverage and film properties at a low temperature.

A Comparative Study on Self‐Aligned Top‐Gate Thin‐Film Transistors with Silicon Nitride as the Interlayer

Thin-film transistors (TFTs) with self-aligned top-gate structure are fabricated, in which the source/drain region is pretreated to be highly conductive during the deposition of silicon nitride as the interlayer. Without deteriorating the properties of the device's channel layer, the basic performance of TFTs can be simply controlled by altering the SiH4 flow rate during the deposition of silicon nitride film. Furthermore, the diffusion of hydrogen dissociated from SiH4 precursor, which can passivate the electron traps at the interface between the channel and dielectric layer or in the bulk of the dielectric layer, can significantly improve the positive bias temperature stress stability. The charge trapping mechanism is verified using the stretched-exponential model, and the rising values of the fitting parameters (ΔVth0 and τ) show that the TFTs stability improves as the flow rate of SiH4 rises. This approach can reduce the cost and simplify the manufacturing of thin-film transistors.

Ultrasensitive UV-C detection based on MOCVD-grown highly crystalline ultrawide bandgap orthorhombic κ-Ga2O3

Orthorhombic κ-Ga2O3, as one of the Ga2O3 polymorphs, is considered a promising as ultrawide bandgap material for extreme environment devices. It is considered more superior than the conventional group III-V compound semiconductors and silicon carbides in extreme environments demanding material/device characteristics of high-voltage, high-temperature, high-pressure, high-impact, and high-radiation. In this study, we demonstrate ultrasensitive ultraviolet-C (UV-C) detection using Si-doped orthorhombic κ-Ga2O3 photodetectors. A 150 nm thick κ-Ga2O3 film was grown on a 2-inch diameter sapphire (α–Al2O3) wafer via metal organic chemical vapor deposition (MOCVD) method. The crystallinity of orthorhombic κ-Ga2O3 film was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The ultrawide bandgap of approximately 4.9 eV was confirmed by UV transmittance measurement. For UV-C detection analysis, a planar device with a channel length of 20 μm was fabricated using Au/Ti metal contacts on the orthorhombic κ-Ga2O3 film. The device doped under 15 sccm SiH4 flow rate showed ultrahigh photoresponse of ∼72.1 A/W, Ion/Ioff of ∼14, and decent rise (∼0.35 s) and decay (∼1.79 s). Our results will contribute to the understanding on a new material phase of κ-Ga2O3, as well as on developing optoelectronics devices with high radiation hardness suitable for operation in extreme environments.

Improved interface and dark current properties of InGaAs photodiodes by high-density N2 plasma and stoichiometric Si3N4 passivation

The interface and dark current properties of mesa-structure In0.83Ga0.17As photodiodes with improved passivation processes are investigated. Inductively coupled plasma chemical vapor deposition (ICPCVD) is used to continuously perform high-density N2 plasma treatment of InGaAs epitaxial material and then SiNx passivation film deposition. The bonding efficiency between Si and N can be effectively improved when close-to-stoichiometric SiNx films are synthesized by precisely controlling the N2 and SiH4 flow rates. Metal-insulator-semiconductor (MIS) capacitors are fabricated to study the interface properties, and C-V analysis shows that the interface state density significantly decreases to 5.3 × 1012 cm−2eV−1. Then, the process is applied to mesa-structure In0.83Ga0.17As photodiodes, and the results show a low dark current density (13 nA/cm2, @ 190 K) and negligible surface current (@ room temperature), indicating the ideal passivation effect. The method of increasing the deposition temperature to promote chemical bonding of SiNx films is studied, and both the interface and dark current properties can be improved. Our work is of important significance to the development of low-noise and large-format InGaAs arrays.

Growth and characterization of PALE Si-doped AlN on sapphire substrate by MOVPE

In this study, we report different SiH4 flow condition effects on crystal, surface, optical, and electrical characteristics of heteroepitaxial Metal-Organic Vapor Phase Epitaxy (MOVPE) grown AlN layers on sapphire substrates. Adjustment of growth kinetics is very important to control the doping. Therefore, pulsed atomic layer epitaxy (PALE) was used to control the growth kinetics and reduce parasitic reactions that inevitably caused adverse impact on the properties of the epitaxial AlN films. As a result of HRXRD (high resolution x-ray diffraction) analysis, the (002) ω FWHM decreased significantly with the PALE method, while the increase occurred due to the development of V defects for the (102) ω scan. Atomic force microscopy (AFM) analyzes showed that SiH4 led to a 3D-like growth mode. It was demonstrated that the increased SiH4 flow increased Si incorporation into the Si-doped AlN layer while increased the sheet resistance due to the self-compensating effect obtained from secondary ion mass spectroscopy (SIMS) and I–V measurement results.

Influence of silane flow rate on the structural and optical properties of GaN nanowires with multiple-quantum-shells

In this study, we discuss the influence of SiH4 flow rates on the structural and optical properties of GaN nanowires (NWs) with multiple-quantum-shells (MQSs). To this end, we prepared two n-GaN core NW samples with different SiH4 flow rates. Subsequently, MQS active layers of the same structure were grown on each n-GaN core NW under identical growth conditions. The samples were characterized by scanning electron microscopy, scanning transmission electron microscopy, energy-dispersive X-ray, and cathodoluminescence (CL) mapping. From the experimental results, we ascertained that a Si-rich layer was created between the sidewall of the NWs and MQSs, in which the number of Si atoms was mainly determined by the SiH4 flow rate. These Si atoms diffused into the MQSs during the growth, and significantly impacted the structural and optical properties, such as the shape and crystalline quality of the MQSs and NWs, and the CL intensity of the MQSs. On the basis of experimental results, we conclude that the SiH4 flow rate during the NW growth plays a critical role in the performance of an MQS-based optoelectronic semiconductor device.

Metalorganic Chemical Vapor Deposition Gallium Nitride with Fast Growth Rate for Vertical Power Device Applications

The development of high‐quality gallium nitride (GaN) epitaxy with thick drift layer, low controllable doping, and high mobility is key for vertical high‐power devices. Herein, the effect of increasing trimethylgallium (TMGa) molar flow rate on the growth rate, impurity incorporation, charge compensation, surface morphology, and carrier mobility is systematically studied. An optimized metalorganic chemical vapor deposition GaN growth condition with a typical growth rate of 2 μm h−1 is used as the baseline. With significant suppression of background Si, other impurity concentrations, and a precise control of the doping precursor SiH4 flow, an electron concentration as low as 4 × 1015 cm−3 in n−‐GaN is achieved. Through increasing the TMGa flow rate, the GaN growth rate is increased to 5.2 μm h−1. Secondary ion mass spectroscopy results show that the background H, O, and Mg remain below detection limit, but C level is increased to 2 × 1016 cm−3. GaN growth on Mn‐doped semi‐insulating GaN substrate is performed to probe the transport properties of film with low dislocation densities. Hall measurement shows that an electron mobility decreases from 852 to 604 cm2 V−1 s−1 as the growth rate increases. Results from this work reveal the challenge and guidance for achieving GaN vertical high power devices.

Легированный кремнием GaSb, выращенный методом ГФЭМОС в широком диапазоне соотношений V/III

Charachterization of Si-doped GaSb epitaxial layers grown by metal organic vapor phase epitaxy is presented. Samples are grown at constant SiH4 flow with a TMSb/TEGa ratio ranged from 1 to 50. X-ray diffraction, Raman scattering, photoluminescence, resistivity, free carrier concentration and their mobility are studied.

Improving Transport Properties of GaN-Based HEMT on Si (111) by Controlling SiH4 Flow Rate of the SiNx Nano-Mask

The AlGaN/AlN/GaN high electron mobility transistor structures were grown on a Si (111) substrate by metalorganic chemical vapor deposition in combination with the insertion of a SiNx nano-mask into the low-temperature GaN buffer layer. Herein, the impact of SiH4 flow rate on two-dimensional electron gas (2DEG) properties was comprehensively investigated, where an increase in SiH4 flow rate resulted in a decrease in edge-type threading dislocation density during coalescence process and an improvement of 2DEG electronic properties. The study also reveals that controlling the SiH4 flow rate of the SiNx nano-mask grown at low temperatures in a short time is an effective strategy to overcome the surface desorption issue that causes surface roughness degradation. The highest electron mobility of 1970 cm2/V·s and sheet carrier concentration of 6.42 × 1012 cm−2 can be achieved via an optimized SiH4 flow rate of 50 sccm.

Atomic layer epitaxy of InAs with high silicon doping concentration

We report on the growth and doping of InAs by atomic layer epitaxy (ALE). The InAs layers were grown using ALE cycles in a metal organic chemical vapor deposition reactor, and Si doping of the films was studied for different SiH4 flow sequences. When SiH4 was added to trimethylindium during the group-III step, the silicon concentration in the film was above 5 × 1019 cm−3. When SiH4 was added to tertiarybutylarsine during the group-V step, much lower incorporation of Si was observed. Conformal Si doped InAs layers were selectively grown by ALE on In0.47Ga0.53As patterned layers made on silicon substrates, demonstrating the suitability of the growth method for III-V device technology on silicon.

Pulsed very high-frequency plasma-enhanced chemical vapor deposition of silicon films for low-temperature (120 °C) thin film transistors

With the aim of improving silicon (Si) film quality deposited by atmospheric-pressure (AP) plasma-enhanced chemical vapor deposition at a low substrate temperature of 120 °C, we examine the difference between continuous wave and pulsed plasmas for deposition characteristics depending on H2 and SiH4 flow rates and inpur VHF power. A specifically designed parallel-plate-type electrode system is used to generate the AP plasma, which is excited by 150 MHz very high-frequency (VHF) electric power. Hydrogen and monosilane diluted with helium are used as the process gases. The electrode system enables us to form turbulence-free one-dimensional gas flow in the plasma zone, thereby ensuring a deposition process without contamination of the substrate surface with dust particles. The electrical property of the deposited Si layers was evaluated by fabricating bottom-gate thin film transistors (TFTs). The performance of the bottom-gate TFTs revealed that the a-Si TFTs, i.e. those channel layers prepared with a pulse duty cycle of 10%, exhibit reasonably high field effect mobilities of around 1 cm2 · V–1 · s–1, suggesting that the pulse modulation of input VHF power is highly effective in achieving a plasma chemistry suitable for high-quality Si growths at low temperatures.

Very low temperature growth of GeSi alloys with digermane, disilane and dichlorosilane

GeSn/GeSi multi quantum wells with (i) high Sn content, direct bandgap GeSn wells and (ii) GeSi barriers with Si contents in the few %–30% range might be of use in optoelectronics. As GeSn has to be grown in the 300–375 °C range (to avoid Sn segregation/precipitation), GeSi barriers should also be grown in that temperature range, too. GeSi might also be used to passivate, at low temperatures, the surface of Ge-rich imagers and photo-detectors. Thanks to X-Ray Reflectivity (thickness) and X-Ray Diffraction (Si content), I have therefore explored, in a 200 mm Chemical Vapour Deposition tool, the 100 Torr growth of tens of nm thick GeSi layers on Ge(001) buffers. Precursor gases were Ge2H6 (Ge), SiH2Cl2 and/or Si2H6 (Si). Whatever the chemistry, a temperature increase in the 350–500 °C range resulted in an increase, (a stabilization) then a decrease of the GeSi growth rate. Meanwhile, the Si content increased almost linearly with the temperature. For given Si and Ge flows, GeSi growth rates were higher and Si contents lower with SiH2Cl2 than with Si2H6. Adding SiH2Cl2 to Si2H6 had, quite surprisingly, almost no impact on the GeSi growth kinetics, which was mainly governed by the Si2H6 flow. With high precursor flows, I succeeded in having, with Ge2H6 and SiH2Cl2, GeSi growth rates increasing from 2 up to 32 nm min−1 as the temperature increased from 325 °C up to 375 °C, with a Si content close to 7.5%. Growth rates increased from 0.6 up to 19 nm min−1 and Si contents decreased from 24 down to 22% over the same temperature range with Ge2H6, SiH2Cl2 and Si2H6.

Selective Growth and Contact Gap-Fill of Low Resistivity Si via Microwave Plasma-Enhanced CVD.

Low resistivity polycrystalline Si could be selectively grown in the deep (~200 nm) and narrow patterns (~20 nm) of 20 nm pitch design rule DRAM (Dynamic Random Access Memory) by microwave plasma-enhanced chemical vapor deposition (MW-CVD). We were able to achieve the high phosphorus (CVD gap-fill in a large electrical contact area which does is affected by line pitch size) doping concentration (>2.5 × 1021 cm−3) and, thus, a low resistivity by adjusting source gas (SiH4, H2, PH3) decomposition through MW-CVD with a showerhead controlling the decomposition of source gases by using two different gas injection paths. In this study, a selective growth mechanism was applied by using the deposition/etch cyclic process to achieve the bottom–up process in the L-shaped contact, using H2 plasma that simultaneously promoted the deposition and the etch processes. Additionally, the cyclic selective growth technique was set up by controlling the SiH4 flow rate. The bottom-up process resulted in a uniform doping distribution, as well as an excellent filling capacity without seam and center void formation. Thus, low contact resistivity and higher transistor on-current could be achieved at a high and uniform phosphorus (P)-concentration. Compared to the conventional thermal, this method is expected to be a strong candidate for the complicated deep and narrow contact process.

Poly-Si/SiOx/c-Si passivating contact with 738 mV implied open circuit voltage fabricated by hot-wire chemical vapor deposition

Hot-wire chemical vapor deposition (HWCVD) was utilized to develop a fast and high quality a-Si:H thin film fabrication method for poly-Si/SiOx carrier selective passivating contacts targeting at n-type passivated emitter rear totally diffused crystalline silicon solar cells. The microstructure and hydrogen content of the a-Si:H thin films were analyzed by Fourier-transform infrared spectroscopy in order to understand the influence of film properties on passivation and conductivity. Dense layers were found to be beneficial for good passivation. On the other hand, blistering appeared as a-Si:H layers became more and more dense. However, by adjusting the SiH4 flow rate and the substrate heater temperature, blistering of a-Si:H could be avoided. A suitable process window was found and firing-stable implied open circuit voltage (iVoc) of up to 738 mV was achieved. In addition to high iVoc, a low contact resistivity of 0.034 Ω cm2 was also achieved. The deposition rate of the a-Si:H layers was 7 Å/s by using HWCVD, which is one order of magnitude higher than the deposition rate reported using other deposition methods.

The changing of silicon suboxide film thickness as a result of high temperature annealing

The a-SiOx:H thin films were deposited by the gas-jet electron beam plasma chemical vapor deposition method with different stoichiometry (x=0.15-1.0) for different SiH4 flow rates. The concentration of hydrogen in the films increases with the growth rate in ranges from 1.5 to 4.8 at.%. Further annealing leads to the effusion of hydrogen from the structure of the material and the compression of the structure, which leads to a reduction in the thickness for all films. X-ray diffraction measurements showed that the as-deposited films crystallized to form nc-Si about 4-8 nm in size after annealing at 1000°C.

Growth and characterization of SiGeSn pseudomorphic layers on 200 mm Ge virtual substrates

In this contribution, we report on the growth of pseudomorphic SiGeSn layers on 2.5 μm thick Ge virtual substrates on Si(001). A single wafer reduced pressure chemical vapor deposition reactor was used for the 100 Torr epitaxy of those layers, with digermane (Ge2H6), tin-tetrachloride (SnCl4) and disilane (Si2H6) as precursors. Detailed analyses regarding the growth kinetics, layer composition and surface morphology as function of the growth temperature and Si2H6 flow are presented. As the temperature increases we have, for the same precursor flows, a Si content increase and a Sn content decrease. The activation energy associated with the exponential increase of the SiGeSn growth rate with the temperature, 9.5 kCal.mol−1, is close to that of GeSn (10.6 kCal.mol−1). Furthermore, we show that the addition of Si2H6 to the gaseous mixture results (besides the expected Si content increase) in a Sn content increase and a Ge content decrease. This study yields a better understanding of the growth of SiGeSn compound semiconductors.