Si In GaN Research Articles

Analysis of useful ion yield for Si in GaN by secondary ion mass spectrometry

The optimum detection levels that can be achieved by a secondary ion mass spectrometer are dependent on how efficiently a particular species of interest can be ionized and detected. One can determine in advance whether the analysis of a particular ion in the sample is possible, if the useful ion yield is known. The useful ion yield depends on the element, instrument transmission, the analytical conditions, the sample matrix, etc. The value of the useful ion yield for a species can diverge from one instrument type to another due to its different transmission and ionization probabilities. However, the same tendencies in the results may be expected for all types of instruments. In this paper, the authors present a quantitative secondary ion mass spectrometry analysis of the useful ion yield for the silicon dopant species in a gallium nitride matrix grown by metal organic chemical vapor deposition. Positively ionized cesium was used as the primary ion beam, and its energy was varied in the range from 0.5 to 5 kV. A quadrupole mass analyzer was utilized to collect secondary ion species of interest. The analysis results can be used to determine the primary beam energies for optimal Si sensitivity.

Demonstration of a 2 kV Al0.85Ga0.15N Schottky Barrier Diode With Improved On-Current and Ideality Factor

In this letter, we report on demonstrating a Schottky barrier diode (SBD) with high reverse blocking voltage by incorporating an ultra-wide bandgap semiconductor Al0.85 Ga0.15 N channel. Benefited from the lower activation energy of the Si in GaN, the net carrier concentration of Al0.85 Ga0.15N can be essentially enhanced to ${2}\times {10}^{{17}}$ cm−3 level with surface roughness of 0.33 nm. Due to the good material property, a reverse blocking voltage of 2 kV and room temperature ideality factor of 2.3 are demonstrated. Combined with the significantly improved on-current and on/off ratio of more than 106 when compared with other AlN SBDs, Al0.85 Ga0.15 N turns out to be a competitive AlN counterpart by considering the compromise among ultra-wide bandgap, dopant activation, and material property.

Local Structure Analysis of Ion Implanted Si in GaN by X-ray Absorption Fine Structure

Local Structure Analysis of Ion Implanted Si in GaN by X-ray Absorption Fine Structure

Doping effects of C, Si and Ge in wurtzite [0001] GaN, AlN, and InN nanowires

We have performed an ab initio investigation, within the spin-polarized density functional theory, of the energetic stability and electronic properties of substitutional Si, Ge, and C impurities in [0001] GaN, AlN, and InN nanowires (NWs). Our total energy results show that C impurities in the cation site (CGa, CAl, and CIn) present lower formation energies at the surface of the NWs as compared to their counterparts in the core of the NW or the bulk system. In these position donor likely properties are obtained for GaN and InN NWs, whereas for the AlN NW deep levels are observed inside the bandgap. In contrast, CN must be distributed uniformly along the NW diameter and gives rise to a deep electronic level inside the NW bandgap. Si in GaN and InN and Ge in InN are most stable at the cation site in the core of the NWs, and lead the systems to show a n-type semiconductor properties. For the AlN NW we obtain that Si and Ge are most likely in a N site at the surface of the NW and introduce deep levels inside the NW bandgap. Meanwhile, C and Ge impurities are amphoteric impurities in GaN NWs.

Study of Si implantation into Mg‐doped GaN for MOSFETs

AbstractIn this paper we focus on activation and diffusion during annealing of silicon after implantation into Mg‐doped GaN epitaxial layers. The Si diffusion was analyzed for different capping materials and compared to an uncapped sample. Investigation of the Si concentration obtained from secondary ion mass spectroscopy (SIMS) and comparison with calculation revealed several diffusion constants. Different diffusion behaviours at the surface were detected for different Si concentrations around the solubility of Si in GaN. Further, we found similar Si activation efficiencies in GaN for high and low fluences, after taking into account the compensation of electrons by the p‐type background doping. In addition, we investigated the insulation between Si implanted islands in p‐type GaN and the effect of additional Ar+ implantation. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Carrier transport and luminescence properties of n-type GaN

The surface morphology, electrical properties and optical properties of Si doped n-type GaN were investigated. The intentional SiH4 doped GaN films were grown by metal organic chemical vapor deposition with the electron concentration varying from 3×1016 cm−3 to 5.4×1018 cm−3. The surface morphology shows that the roughness and dislocation pits increase as the mass flow rate of SiH4 increases, which indicates that the quality of GaN degrades gradually. The activation energy of Si in GaN with different n concentrations varies from 12 to 22 meV, which may originate from the interactions of donor wave functions. The carrier transport mechanism with increasing temperature from 100 to 420 K was concluded as the complex effect of both impurity scattering and phonon scattering. The position of the near band edge emission peak was determined by both renormalization of the band gap and B-M effect. The intensity variations of the yellow luminescence could be explained by the change of Ga vacancy concentration caused by Si doping.

Silicon behavior in GaN grown by radiofrequency plasma molecular beam epitaxy

The behavior of Si in GaN has been investigated in the wide doping range from 1×10 17 to 9×10 19 cm −3 by photoluminescence (PL). PL studies at 77 K for doped specimens show that the intensity of the near-band-edge emission increased monotonically as the Si concentration increases. The intensity of the yellow luminescence (YL), however, remains almost constant, which indicates that Si does not strongly influence the density of deep centers in GaN. The red-shift of the near-band-edge emission due to increase the Si concentration shows that bandgap renormalization (BGR) effect is much more important than the Burstein–Moss (B-M) effect in Si-doped GaN. With Si doping as high as 9×10 19 cm −3, a new peak due to donor-to-acceptor recombination appears in the PL spectrum. This donor-to-acceptor emission peak can also be observed in the PL spectrum of Si-doped GaN after thermal annealing. We attributed the appearance of the new acceptor level to the formation of Si N. A model has been proposed to illustrate the Si behavior in GaN in a wide range of Si concentrations.

In situ studies of the effect of silicon on GaN growth modes

We present real-time X-ray scattering studies of the influence of silicon on the homoepitaxial growth mode of GaN grown by metal-organic vapor-phase epitaxy. Both annealing of Si-doped GaN and surface dosing of GaN with disilane are shown to change the mode of subsequent growth from step-flow to layer-by-layer. By comparing the growth behavior induced by doped layers which have been annealed to that induced by surface dosing, we extract an approximate diffusion coefficient for Si in GaN of 3.5 ×10 −18 cm 2/ s at 810°C.

Local microstructures of Si in GaN studied by x-ray absorption spectroscopy

Si K-edge x-ray absorption spectroscopy (XAFS) has been used to study the local structure of Si dopant in GaN crystalline material. Doping concentrations NSi from 8.0×1016 to 4.4×1019 cm−3 were investigated. It is observed that the near-edge spectra vary significantly as a function of NSi. At low concentrations the Si K-edge spectra exhibit features similar to that obtained from N K-edge measurement, while at high concentrations the near-edge spectra shape is similar to that recorded from Si3N4. We interpret the results as an indication that Si is not randomly distributed. The changes of the near-edge spectra as a function of doping level is explained as due to changes in the magnitude of Si local lattice contraction caused by the formation of various types of Si clusters. The interpretation is further supported by extended XAFS spectra analysis. A Si-induced strain-field near the surface is proposed as the main force for the cluster formation during epitaxial growth.

Delta-Doping of Si in GaN by Metalorganic Chemical Vapor Deposition

Si delta-doping in the GaN layer has been successfully demonstrated by metalorganic chemical vapor deposition. From the capacitance-voltage measurement, a sharp carrier concentration profile with a full width at half-maximum of 4.1 nm has been achieved with a peak concentration of 9.8×1018 cm-3. Si delta-doping concentration increases and then decreases with an increase in delta-doping time, and the use of a post-purge step in the ammonia ambient reduces Si delta-doping concentration. This indicates that delta-doping concentration is limited by the Si desorption process due to high growth temperatures.

Lattice location of Si in ion implanted GaN

The lattice location of Si in GaN has been investigated by ion channeling in combination with Rutherford backscattering spectrometry, particle induced x-ray emission, and nuclear reaction analysis. Metalorganic chemical vapor deposition grown GaN on c-plane sapphire substrates and implanted with Si28 at a dose of 7×1014 cm−2 with postimplant annealing were investigated. It was found that almost 100% of Si goes into the Ga site at 1100 °C. Our results directly indicate that the electrical activation of Si implanted GaN with postimplant annealing is due to the formation of substitutional Si at this temperature.

Si in GaN — On the Nature of the Background Donor

AbstractA characterization of the Si impurity in GaN is performed by Raman spectroscopy. Applying hydrostatic pressure up to 25 GPa we study the behavior of the LO phonon‐plasmon mode in a series of high mobility Si doped GaN films. In contrast to earlier results on unintentionally doped bulk GaN crystals no freeze out of the free carriers could be observed in Si doped samples. We find that Si is a shallow hydrogenic donor throughout the pressure range studied. This result positively excludes Si incorporation as a dominant source of free electrons in previously studied bulk GaN samples.

Secondary-ion mass spectroscopy (SIMS) investigations of Be and Si incorporation in GaN grown by molecular beam epitaxy (MBE)

We have studied the incorporation of Be and Si in GaN grown using molecular beam epitaxy (MBE). From secondary-ion mass spectroscopy (SIMS) measurements, Be was found to have an enhanced diffusion rate at high concentration similar to the behaviour observed previously in GaAs. On the other hand, Si behaves as a conventional n-type dopant with no evidence from SIMS for either segregation or diffusion out of the layer. For Be-incorporated material we report new lines in the PL spectrum for both wurtzite and zinc blende polytypes, and we suggest that Be may be a suitable dopant for the zinc blende material.

On Compensation and Impurities in State-of-the-Art GaN Epilayers Grown on Sapphire

ABSTRACTA comparison between 300 K electron transport data for state-of-the-art wurtzite GaN grown on sapphire substrates and corresponding theoretical calculations shows a large difference, with experimental mobility less than the predicted mobility for a given carrier concentration. The comparison seems to imply that GaN films are greatly compensated, but the discrepancy may also be due to the poorly known values of the materials parameters used in the calculations. In this work, recent analysis of transport and SIMS measurements on silicon-doped GaN films are shown to imply that the compensation, NA/ND, is less than 0.3. In addition, the determination of an activation energy of 34 meV in a GaN film doped to a level of 6×1016 cm−3 suggests either that a second, native donor exists in the doped films at a level of between 6×1017 cm−3 and 1×1017 cm−3, or that the activation energy of Si in GaN is dependent on the concentration, being influenced by impurity banding or some other physical effect. GaN films grown without silicon doping are highly resistive.