SiC Heterostructures Research Articles

A study of the intermediate layer in 3C–SiC/6H–SiC heterostructures

Transmission electron microscopy and the cathodoluminescence method have been used to study the transition region in 3C–SiC/6H–SiC heterostructures. It is shown that this region is, as a rule, constituted by alternating 3C–SiC and 6H–SiC layers, with possible inclusion of other silicon carbide polytypes. An assumption is made that this structure of the transition region can be explained in terms of the spinodal decomposition model.

Ni/n-Si/N+-SiC Heterostructure Schottky Barrier Photodiode Used in Non-ultraviolet Region

Due to the wide bandgap of SiC, SiC-based photoelectric devices can be only driven by ultraviolet light, which essentially limit its application for a detection of visible and infrared light. In order to realize the non-UV operation of the SiC-based photoelectric devices applied in high temperature and high power regions, Ni/n-Si/N+-SiC heterostructure Schottky barrier photodiode has been studied. Energy-band structure of the Ni/n-Si/N+-6H-SiC structure was simulated by Silvaco-TCAD. And the non-UV photodiode with this structure was fabricated on 6H-SiC(0001) substrate. J-V measurements indicate that the device has good rectifying behavior with a rectification ratio up to 200 at 5V, and the turn-on voltage is about 0.7V. Under non-ultraviolet illumination of 0.6W/cm2, the device demonstrates significant photoelectric response with a photocurrent density of 2.9mA/cm2 and an open-circuit voltage of 63.0mV. Non- ultraviolet operation of the SiC-based photoelectric device is initially realized.

Lattice-matching of Si grown on 6H–SiC(000−1) C-face

Si films with <111> preferred orientation have been prepared on 6H–SiC(000−1) C-face. HRTEM and SAED results indicate that the Si film has epitaxial connection with the 6H–SiC substrate and the parallel-plane relationship of the Si/6H–SiC heterostructure is (111)Si//(000−1)6H–SiC. Using fast Fourier transform and Fourier mask filtering technique, misfit dislocations are clearly observed at the Si/6H–SiC interface, which accommodate the most of lattice mismatch strain. Every four Si (111) lattice planes are registered with five 6H–SiC(000−1) lattice planes along the interface. Based on the 4:5 lattice matching mode, the lattice structure of the Si/6H–SiC interface and its stability were energetically investigated by molecular dynamics simulations. When the Si films grow preferentially along <111> orientation on 6H–SiC(000−1) C-face, the misfit strain in Si layer significantly reduces due to the relaxation of C atoms in SiC layer near the Si/6H–SiC interface, and thus the Si/6H–SiC heterostructure has a stable interface with a small interface formation energy of −14.24eV.

Magnetotransport properties of two-dimensional electron gas in AlGaN/AlN/GaN heterostructures

Magnetotransport measurements are carried out on the AlGaN/AlN/GaN in an SiC heterostructure, which demonstrates the existence of the high-quality two-dimensional electron gas (2DGE) at the AlN/GaN interface. While the carrier concentration reaches 1.32×1013 cm−2 and stays relatively unchanged with the decreasing temperature, the mobility of the 2DEG increases to 1.21×104 cm2/(V·s) at 2 K. The Shubnikov—de Haas (SdH) oscillations are observed in a magnetic field as low as 2.5 T at 2 K. By the measurements and the analyses of the temperature-dependent SdH oscillations, the effective mass of the 2DEG is determined. The ratio of the transport lifetime to the quantum scattering time is 9 in our sample, indicating that small-angle scattering is predominant.

ZnO epitaxy on SiC( [formula omitted]) substrate: Comparison with ZnO/SiC(0 0 0 1) heterostructure

ZnO thin layers deposited on 6H–SiC substrates showed six-fold crystal symmetry with an epitaxial relationship of (0 0 0 2) ZnO||(0 0 0 6) SiC and [ 1 1 2 ¯ 0 ] ZnO||[ 1 1 2 ¯ 0 ] SiC. Despite the different 6H–SiC substrate surface orientations for the ZnO epitaxy, the orientation relationship of ZnO/6H–SiC heterostructures is identical, as confirmed by X-ray diffraction studies. In these ZnO/6H–SiC(0 0 0 1) and ZnO/6H–SiC( 0 0 0 1 ¯ ) heterostructures, the valence band offsets are measured to be 1.12 eV and 1.09 eV, leading to the conduction band offset values of 0.75 eV and 0.72 eV, respectively. These slightly different band-offset values in ZnO/6H–SiC heterojunctions are attributed to the variation of valence band maximums and the different interface charge compensation mechanisms.

N-Al0.15Ga0.85 N/p-6H–SiC heterostructure and based bipolar transistor

Heterojunction bipolar transistor (HBTs) based on Al0.15Ga0.85 N/6H–SiC heterojunction was fabricated. Room-temperature current–voltage ( I– V) characteristics of n-Al0.15Ga0.85 N/p-6H–SiC emitter–base heterojunction exhibited good rectifying behavior with a forward current 5 × 10 −2 A and reverse current 3 × 10 −9 A at 10 V and −10 V, respectively. Analysis of the temperature dependent I– V characteristics of this heterojunction revealed a barrier height of 1.1 eV. The fabricated n-Al0.15Ga0.85 N/p-SiC/n-SiC bipolar transistor did not exhibit common-emitter operation, however, common-base operation was observed with current gain β = IC/ IB ranging in 75–100.

Negative magnetoresistance in SiC heteropolytype junctions

In this study, we carried out for the first time a galvanomagnetic investigation of 3C–SiC/6H–SiC heterostructures at liquid-helium temperatures and observed in n-3C–SiC low resistance of the samples and the appearance of a negative magnetoresistance in weak fields (~1 T). Analysis of the results we obtained shows that the low resistance is in all probability due to a metal—insulator transition in 3C–SiC epitaxial films. It was also found that the negative magnetoresistance magnitude decreases as the density of intertwine boundaries in a 3C–SiC epitaxial film becomes lower.

Formation of silicon carbide nanocrystals by high-temperature carbonization of porous silicon

Based on X-ray diffraction analysis, Auger spectroscopy, and Raman scattering, it is shown that carbonization of porous silicon at temperatures of 1200–1300°C results in formation of silicon carbide nanocrystals 5–7 nm in size. The growth of 3C-SiC nanocrystals of fixed size d proceeds as follows. Silicon nanocrystals with d = 3–7 nm pass into the liquid phase, thereby effectively participating in the growth of silicon carbide. After the size of a crystallite has achieved a critical value determined by the equality of its melting point and environmental temperature, the crystallite solidifies and virtually ceases to grow. As a result, a nanocrystalline Si-SiC-amorphous SiC heterostructure is obtained.

Process control and melt depth homogenization for SiC-on-Si structures during flash lamp annealing by carbon implantation

Flash lamp annealing in the millisecond regime of heteroepitaxial silicon carbide on silicon structures involves melting the silicon below the SiC layer, but the deep faceted nature of the liquid-solid interface leads to unacceptable surface roughness. This paper describes a method of controlling melting by implanting a high dose of carbon at a controlled depth below the Si∕SiC interface, which significantly alters the melting characteristics of the silicon. This technology has also been applied to SiC and Si multilayer heterostructures. Results confirm the effectiveness of this approach for increasing surface uniformity, making liquid phase processing compatible with standard device fabrication techniques. A thermal model has also been developed to describe this process and results indicate that the theoretical work is consistent with the experimental evidence. The model is a valuable tool for predicting the onset of melting, maximum temperatures, and process windows for controlled liquid phase epitaxy.

6H(n&lt;sup&gt;+&lt;/sup&gt;)/3C(n)/6H(p&lt;sup&gt;+&lt;/sup&gt;) - SiC Structures Grown by Sublimation Epitaxy

Investigation of the multilayer 6H(n+)/3C(n)/6H(p+)-SiC heterostructure grown by sublimation epitaxy show that the injection electroluminescence (IEL) in the green region (hνmax≈2.30-2.35eV) of spectrum is dominant. This band is close to the electroluminescence peak due to defects in 6H-SiC but also can be due to free exciton annihilation in a quantum well in 3C-SiC at the 6H/3C-SiC heterointerface. At high current the IEL peak at hνmax≈2.9 eV is found. This peak (and also two another peaks in blue part of spectra: hνmax≈2.6 eV and hνmax≈2.72 eV) can be attributed to recombination in 6H-SiC. The forward current-voltage characteristics for best structures are close to those for ideal 6H-SiC pn homostructure and characterized by abrupt breakdown. A lot of structures are characterized by barrier type excess current. Structure in the region of evident 3C-SiC inclusion is characterized by high forward and reverse excess currents.

Impact of surface treatment under the gate on the current collapse of unpassivated AlGaN/GaN heterostructure field-effect transistors

Unpassivated GaN/AlGaN/GaN/SiC heterostructure field-effect transistors were fabricated on intentionally undoped and 5 × 1018 cm−3 modulation-doped material structures. The influence of surface treatment before gate metallization on the gate leakage and drain current collapse of the devices was observed. In the case of a short HCl treatment (∼5 s), a relatively small gate leakage (<10−6 A mm−1 at −6 V gate bias) but large current collapse (∼30% after applying 5 µs wide pulses) were measured. On the other hand, devices with a longer surface treatment (15–20 s) showed an increased gate leakage (>10−4 A mm−1) and a simultaneously negligible current collapse (<5%). This effect is qualitatively similar in devices prepared on the undoped and doped heterostructures. It is assumed that a thin interfacial oxide layer under the gate might be responsible for a lower leakage current and a larger current collapse of the devices.

Traps in AlGaN∕GaN∕SiC heterostructures studied by deep level transient spectroscopy

AlGaN ∕ GaN ∕ SiC Schottky barrier diodes (SBDs), with and without Si3N4 passivation, have been characterized by temperature-dependent current-voltage and capacitance-voltage measurements, and deep level transient spectroscopy (DLTS). A dominant trap A1, with activation energy of 1.0 eV and apparent capture cross section of 2×10−12cm2, has been observed in both unpassivated and passivated SBDs. Based on the well-known logarithmic dependence of DLTS peak height with filling pulse width for a line-defect related trap, A1, which is commonly observed in thin GaN layers grown by various techniques, is believed to be associated with threading dislocations. At high temperatures, the DLTS signal sometimes becomes negative, likely due to an artificial surface-state effect.

Electrical and Optical Properties of n-ZnO/p-SiC Heterojunctions

A series of n-ZnO/p-6H–SiC heterostructures have been grown by molecular-beam epitaxy, and electrical and optical properties of the mesa diodes have been studied. Current versus voltage (I–V) characteristics of the samples revealed a good rectifying behavior of all samples with a typical leakage current less than 10-7 A at -8, and with forward currents changing from sample to sample and at 8 V lying in the range 0.8–10 mA. Capacitance–voltage (C–V) profiles and double pulse deep level transient spectroscopy (DDLTS) indicate interface states in the 1012–1013/cm2 eV range, sharply peaked below 0.5 eV. Under forward bias electroluminescence (EL) emission was observed from most of the samples in yellow and violet regions with maxima at ∼2.1 and ∼2.92 eV, which attributed to the SiC side of the n-ZnO/p-6H–SiC heterojunction, from the comparison with the photoluminescence spectra of n-ZnO and p-SiC.

Mismatched Heteroepitaxy of Tetrahedral Semiconductors with Si via ZrB2 Templates

We demonstrate integration of cubic SiC (heterostructures and nanostructures) and assemblies of Ge nanoscale islands with Si substrates via a conductive and reflective ZrB2 buffer layer. Hexagonal ZrB2 is grown on cubic Si(111) via a coincidence-misfit mechanism in which the strain is accommodated by edge dislocations along the interface. Ge islands with uniform sizes and strain-free microstructures were grown on ZrB2/Si(111) at 500 °C via thermolysis of Ge2H6, circumventing the strain-driven (Stranski−Krastanov) island formation on Si and associated limitations. Heteroepitaxy between ZrB2(0001) and Ge(111) is obtained via alignment of four lattice rows of Ge with every five rows of ZrB2, (i.e., “magic mismatch”) despite the large difference in lattice constants. Cubic SiC layers with monocrystalline microstructures and atomically abrupt interfaces are grown on ZrB2/Si(111) via single source molecular beam epitaxy of C2(SiH3)2 at 800 °C. Nanoscale SiC islands with perfectly coherent zinc blende structures...

Formation of two-dimensional electron gases in polytypic SiC heterostructures

The formation of two-dimensional electron gases (2DEGs) at polytypic (hexagonal/cubic) SiC heterojunctions (4H/3C SiC and 6H/3C SiC) is investigated by numerical self-consistent solutions of the Schrödinger and Poisson equations. The free-electron-density distributions and conduction-band profiles in the SiC heterostructures are calculated and compared to those occurring at AlGaN/GaN interfaces. Spontaneous and piezoelectric polarization effects in both SiC/SiC and AlGaN/GaN structures are taken into account. The combined effect of the polarization-induced bound charge and conduction-band offset between the hexagonal and cubic SiC polytypes results in the formation of 2DEGs with very high electron sheet concentration. 2DEG sheet densities about 20% larger than that in Al0.3Ga0.7N/GaN structures are calculated for 4H/3C SiC heterostructures. We also find that the 2DEG densities in the 4H/3C are much less sensitive to variations of the barrier layer thickness. The influence of the barrier doping layer on the 2DEG densities is also investigated.

Band structure and alignment of the AlN∕SiC heterostructure

Valence-band structures and band alignments at the AlN∕SiC interface are studied by x-ray photoelectron spectroscopy (XPS) combined with first-principle calculations. Theoretical valence-band structures of SiC and AlN, and band offsets at their interface, were obtained by plane-wave pseudopotential method within the framework of density functional theory. The conduction- and valence-band offsets determined by XPS are 1.3 and 1.7eV, respectively, in excellent agreement with the theoretical values. These relatively large band offsets indicate that AlN is suitable as a gate dielectric or a lattice-matched interfacial layer on SiC.

Current transport property of n-GaN∕n-6H–SiC heterojunction: Influence of interface states

Heterostructures of n-GaN∕n-6H–SiC grown by hydride vapor phase epitaxy (HVPE) and molecular-beam epitaxy (MBE) are characterized with the current–voltage (I–V), capacitance–voltage (C–V), and deep level transient spectroscopy (DLTS) techniques. Using different contact configurations, the I–V results reveal a rectifying barrier in the n-GaN∕n-6H–SiC heterostructures. When GaN is negatively biased, the current is exponentially proportional to the applied voltage with the built-in barrier being 0.4–1.1eV for the HVPE samples and 0.5eV for the MBE sample. DLTS measurements reveal intense band-like deep level states in the interfacial region of the heterostructure, and the Fermi-level pinning by these deep level defects is invoked to account for the interfacial rectifying barrier of the heterostructures.

Structural studies on ion-implanted semiconductors using X-ray synchrotron radiation: Strain evolution and growth of nanocrystals

X-ray synchrotron radiation is a very powerful tool in structural analysis of solids. Due to its extremely high intensity and low angular divergence, synchrotron radiation allows for the study of structures that otherwise is impossible. Here, the typical studies on different semiconductor materials using various methods of synchrotron X-ray scattering are presented. Ion implantation in compound semiconductors is a quite complicated process leading to some usually detrimental effects like buildup of damage and strain. In the case of InP, produced strain is rather low and is hardly accessible by the conventional X-ray analysis. InP single crystals implanted with different doses of 1.2 MeV As + ions were studied. It was found that implanted layers are under tensile stress, which relaxes upon prolonged storage at RT. Another important issue is the analysis of nanocrystals. Diamond–SiC heterostructures produced by ion beam synthesis are considered as a promising technique for production of novel devices for high-power applications. Synthesized by ion bombardment nanocrystals that grow in the single crystalline matrix are highly oriented. As revealed by X-ray scattering, size and shape of nanocrystals, as well as incorporated strain depend on the ion implantation parameters.

Accurate Lattice Constant and Mismatch Measurements of SiC Heterostructures by X-Ray Multiple-Order Reflections

ABSTRACTHigh-resolution X-ray diffraction (HRXRD) combined with other diffraction techniques is applied to characterize 3C SiC epilayers hoteroepitaxially grown on atomically flat mesas on 4H and 6H SiC substrates. Small-beam rocking curve scan and reciprocal mapping show extremely high crystalline perfection and homogeneity of the ideally grown 3C-SiC epilayers. Accurate lattice measurements based on X-ray multiple-order reflections reveal that: 1) no misorientation between the (0001) lattice planes across the 4H/3C or 6H/3C interface is detected, confirming the 2D nucleation mechanism of the 3C epilayer from a flat coherent interface; 2) in-plane substrate/epilayer lattice mismatch always exists, but the 3C epilayers do not correspond to a completely relaxed cubic structure, indicating that the epilayers are partially strained; 3) lattice mismatch varies for different regions, implying a complicated strain relaxation mechanism of 3C epilayers on various mesas.

LSP image sensors based on SiC heterostructures

A newly engineered ZnO:Al/a-p–i–n Si x C 1 − x :H/Al configuration for the laser scanner photodiode (LSP) imaging detector is proposed and the read-out parameters improved. The effect of the sensing element structure and light source flux are investigated and correlated with the sensor output characteristics. When wide band gap doped layers are used, data reveals an increased image signal optimised to the blue, a dynamic range of two orders of magnitude, a sensitivity of 6 mA/W and a responsivity of 170 μW cm −2 at 530 nm. The main output characteristics such as image responsivity, resolution, linearity and dynamic range were analysed under reverse, and forward bias and short circuit mode. Results show that in a wide range of incident light power, the sensor performance are optimised in short circuit mode. A trade-off between read-out parameters and the required sensor characteristics is needed to minimise the cross talk between dark and illuminated regions.