Papers by Keyword: Deep Level

Abstract: We demonstrate 4H-SiC bipolar junction transistors (BJTs) with an enhanced current gain over 250. High current gain was achieved by utilizing optimized device geometry as well as optimized surface passivation, continuous epitaxial growth of the emitter-base junction, combined with an intentional deep-level-reduction process based on thermal oxidation to improve the lifetime in p-SiC base. We achieved a maximum current gain (β) of 257 at room temperature and 127 at 250°C for 4H-SiC BJTs fabricated on the (0001)Si-face. The gain of 257 is twice as large as the previous record gain. We also demonstrate BJTs on the (000-1)C-face that showed the highest β of 439 among the SiC BJTs ever reported.

Abstract: This paper is a summary of the experimental study of deep levels in a SiC crystal lattice caused by diffusion welding (DW). Investigations were carried out by DLTS and Kelvin Probe methods. Investigations revealed that DLTS method is not applicable for identification of surface states. Research conducted by the Kelvin Probe method has shown an increase in the density of surface states after the diffusion welding from 2x10¹⁵ cm^-2 to 3.5x10¹⁶ cm^-2.

Abstract: Deep-level defects in 4H-SiC Schottky diodes were studied using deep level transient spectroscopy (DLTS). The epitaxial layers, doped with N and grown on standard n+4H-SiC substrates were exposed to aluminium ion implantation process under the Schottky contact and of junction termination extension (JTE). The studies performed within 80-400 K temperature range revealed five deep electron traps, with a dominant double peak at around room temperature related to the Z1/Z2 defect. The thorough analysis of the DLTS-line shape and DLTS-line behaviour on DLTS measurement conditions made possible to distinguish and identify all the observed deep levels.

Abstract: We investigate self-assembled pyramid-shaped Ge Quantum Dots (QDs) with lateral dimensions of 15 nm, and heights of 2.5-3 nm. These Ge QDs were grown by Molecular Beam Epitaxy (MBE) on n-type Si(100) substrates using the Sb-mediated growth mode. The resistivity of the substrates was about 5 Ωcm. The Si buffer layer below the QDs and the Si capping layer above them were doped up to 10¹⁸ cm^-3 by Sb. Cross-section transmission electron microscopy shows the QDs and the Sb delta-doped layers. Using standard photolithographic techniques, a 0.3 mm² Au Schottky contact was applied to the epilayer, while an Ohmic contact was formed on the back side of the substrate. Plotting C^-2 vs. V plot reveals the nominal doping of 10¹⁸ cm^-3. DLTS studies revealed two levels with fitted activation energies of 49 meV and 360-390 meV. They are related to the Sb doping and the Pb interface states, respectively. The simulation suggests a deep level with a volumetric concentration of 2.55×10¹⁵ cm^-3. Multiplying this value by the thickness of the depletion region obtained from the CV measurements, we find that the deep level capture about 5.8×10⁹ electrons per cm².

Abstract: The electrical properties of dome-shaped and pyramid-shaped Ge Quantum Dots (QDs) embedded in p-type Silicon are reported. Capacitance-Voltage (T-CV) characteristics are reported for the temperature range of 35 K to 296 K. The T-CV results showed the desired charge carrier density of the Silicon, on the order of 10¹⁶ cm^-3, at room temperature. Two shoulders are observed in the CV curves between 270 K and 175 K. They are explained as charge stored in the dome- and pyramid-shaped QDs. Below 175 K, only one shoulder is observed in the CV measurements, attributed to charge trapped in dome-shaped QDs. The DLTS study confirms these results. Using a reverse bias between -0.1 V and -1 V two peaks are seen at 50 and 70 K. They are explained in terms of the boron state (the one at 50 K) and charged stored on pyramid-shaped Ge QDs (the one at 70 K). Increasing the reverse bias from -1 V to -1.4 V shows the appearance of a peak around 60 K, attributed to dome-shaped Ge QDs. At the same time, a shoulder appears around 100 K for -1 V, which extends to larger temperatures as the reverse bias magnitude is increased. The activation energies found are around 50 meV (due to Boron), 150 to 250 meV (due to pyramid-shaped Ge QDs), 300 to 350 meV (due to dome-shaped Ge QDs) and 425 meV (due to both dome- and pyramid-shaped Ge QDs).

Abstract: In the present paper, 4H-SiC JBS diodes with "boron" p–n junctions have been investigated by means of deep-level transient spectroscopy (DLTS). The sign of the DLTS signal for all the 4H-SiC diodes under study, was positive. The "anomaly" of the DLTS spectra measured is apparently connected with the properties of "boron" p–n junctions. In particular, is presented the role of deep D-centers in recompensation of donors in the JBS diodes.

Abstract: We have studied the electrical properties of Si p-n junction diodes by deep level transient spectroscopy (DLTS) measurements. The p-n junctions were developed on a Phosphorus doped Si by depositing Al and annealing at various temperatures. In order to confirm junction formation, current-voltage and capacitance-voltage measurements were made. Two deep levels at Ec-0.17 eV (E1) and Ec-0.44 eV (E2) were observed in the DLTS spectrum. These traps have been characterized by their capture cross-section, activation energy level and trap density. On the basis of these parameters, level E1 can be assigned as V-O complex and E2 as P-V complex. These traps are related to the growth of n-Si wafer and not due to Al diffusion.

Abstract: Electron paramagnetic resonance (EPR) at X-band (9.4 GHz) and Q-band (35 GHz) have been used to study defects in two samples of AlN monocrystals, grown by a sublimation sandwich method. These investigations reveal the presence of Fe2+ impurities in the reddish sample. The spectra of substitutional Fe2+ are highly anisotropic and could be observed even up to the room temperature. After illumination the signals showing the DX behavior were detected in the same sample. We assume these signals to arise due to the presence of the shallow donor center namely the isolated substitutional oxygen ON occupying the nitrogen position. In the second slightly amber-coloured sample EPR measurements before and after X-ray showed the presence of a deep-donor center which was assumed to be nitrogen vacancy VN. Based on thermoluminescence measurements the depth of the level was estimated to 0.45-0.5 eV.

Abstract: The authors have investigated effects of thermal oxidation on deep levels in the whole energy range of bandgap of 4H-SiC which are generated by ion implantation, by deep level transient spectroscopy (DLTS). The dominant defects in n-type samples after ion implantation and high-temperature annealing at 1700oC, IN3 (Z1/2: Ec – 0.63 eV) and IN9 (EH6/7: Ec – 1.5 eV) in low-dose-implanted samples, can be remarkably reduced by oxidation at 1150oC. However, in p-type samples, the IP8 (HK4: Ev + 1.4 eV) survives and additional defects, several defects such as IP4 (HK0: Ev + 0.72 eV) appear after thermal oxidation in low-dose-implanted samples. The defects except for the IP8 center can be reduced by subsequent annealing at 1400oC. These phenomena are explained by a model that excess interstitials are generated at the oxidizing interface and diffuse into the bulk region.

Abstract: In this study, deep levels are investigated, which are introduced by reactive ion etching (RIE) of n-type/p-type 4H-SiC. The capacitance of as-etched p-type SiC is remarkably small due to compensation or deactivation of acceptors. These acceptors can be recovered to the initial concentration of the as-grown sample after annealing at 1000oC. However, various kinds of defects remain at a total density of ~5× 1014 cm-3 in a surface-near region from 0.3 μm to 1.0 μm even after annealing at 1000oC. The following defects are detected by Deep Level Transient Spectroscopy (DLTS): IN2 (EC – 0.35 eV), EN (EC – 1.6 eV), IP1 (EV + 0.35 eV), IP2 (HS1: EV + 0.39 eV), IP4 (HK0: EV + 0.72 eV), IP5 (EV + 0.75 eV), IP7 (EV + 1.3 eV), and EP (EV + 1.4 eV). These defects generated by RIE can be significantly reduced by thermal oxidation and subsequent annealing at 1400oC.