N. Nordell

Ionization rates and critical fields in 4H silicon carbide

Epitaxial p-n diodes in 4H SiC are fabricated showing a good uniformity of avalanche multiplication and breakdown. Peripheral breakdown is overcome using the positive angle beveling technique. Photomultiplication measurements were performed to determine electron and hole ionization rates. For the electric field parallel to the c-axis impact ionization is strongly dominated by holes. A hole to electron ionization coefficient ratio of up to 50 is observed. It is attributed to the discontinuity of the conduction band of 4H SiC for the direction along the c axis. Theoretical values of critical fields and breakdown voltages in 4H SiC are calculated using the ionization rates obtained.

Deep Defect Centers in Silicon Carbide Monitored with Deep Level Transient Spectroscopy

Electrical data obtained from deep level transient spectroscopy investigations on deep defect centers in the 3C, 4H, and 6H SiC polytypes are reviewed. Emphasis is put on intrinsic defect centers observed in as-grown material and subsequent to ion implantation or electron irradiation as well as on defect centers caused by doping with or implantation of transition metals (vanadium, titanium, chromium, and scandium).

Deep level defects in electron-irradiated 4H SiC epitaxial layers

Deep level defects in electron-irradiated 4H SiC epitaxial layers grown by chemical vapor deposition were studied using deep level transient spectroscopy. The measurements performed on electron-irradiated p+n junctions in the temperature range 100–750 K revealed several electron traps and one hole trap with thermal ionization energies ranging from 0.35 to 1.65 eV. Most of these defects were already observed at a dose of irradiation as low as ≈5×1013 cm-2. Dose dependence and annealing behavior of the defects were investigated. For two of these electron traps, the electron capture cross section was measured. From the temperature dependence studies, the capture cross section of these two defects are shown to be temperature independent.

Investigation of aluminum nitride grown by metal–organic chemical-vapor deposition on silicon carbide

Undoped single crystalline aluminum nitride films were grown on 4H and 6H SiC substrates using metal–organic chemical-vapor deposition at 1200 °C. From in situ reflection high-energy electron diffraction, x-ray diffraction rocking curves, and cathodoluminescence spectra, the crystallinity of the films was confirmed. Atomic force microscopy showed that some films were substantially dominated by island growth, rather than step flow growth. Aluminum was evaporated to form metal–insulator–semiconductor (MIS) capacitors for high-frequency capacitance voltage measurements carried out at room temperature. Low leakage made it possible to measure the structures and characterize accumulation, depletion, deep depletion, and, in some cases, inversion. From independent optical thickness measurements, the relative dielectric constant of aluminum nitride was confirmed at 8.4. The flatband voltage of the AlN MIS capacitors on p-type SiC was close to the theoretical value expected. The films were stressed up to 60 V (3 MV...

ELECTRICALLY ACTIVE POINT DEFECTS IN N-TYPE 4H-SIC

An electrically active defect has been observed at a level position of ∼ 0.70 eV below the conduction band edge (Ec) with an extrapolated capture cross section of ∼ 5×10−14 cm2 in epitaxial layers ...

Transient enhanced diffusion of implanted boron in 4H-silicon carbide

Experimental evidence is given for transient enhanced diffusion of boron (B) in ion-implanted silicon carbide (SiC). The implanted B is diffusing several mu m into the samples when annealed at 1600 ...

Temperature dependence of avalanche breakdown for epitaxial diodes in 4H silicon carbide

The temperature dependence of avalanche breakdown is investigated for uniform and microplasma-related breakdown in epitaxial 4H SiC p-n junctions. P-n mesa diodes fabricated with positive angle beveling and oxide passivation can withstand temperatures of up to 300–400 °C in the breakdown regime. Uniform avalanche breakdown in 4H silicon carbide appears to have a positive temperature coefficient, in contrast to the 6H polytype, where the temperature coefficient is negative. The influence of deep levels on avalanche breakdown in epitaxial diodes is of minor importance for uniform breakdown, but appears to be significant for breakdown through microplasmas. A negative temperature coefficient for the avalanche breakdown voltage can be observed even for 4H SiC if the breakdown is dominated by microplasmas.

Diffusion of Zn and Mg in AlGaAs/GaAs structures grown by metalorganic vapor-phase epitaxy

The diffusion of thin, highly p‐doped layers in AlGaAs/GaAs single‐ and double‐heterostructures, grown by metalorganic vapor‐phase epitaxy, was studied with C‐V etch profiling and secondary ion mass spectroscopy. The effect of different post‐growth heat treatments was investigated and diffusion coefficients for both magnesium and zinc were measured. It was found that Mg diffuses about twice as fast Zn and that the order of magnitude of the diffusion coefficient is 10−14 cm2 s−1 at 900 °C, the exact value being process and concentration dependent. A model based on the interstitial–substitutional diffusion mechanism with suitable kinetic limitations was successfully used to simulate the observed dopant concentration profiles.We also found an anomalous strong diffusion of zinc from GaAs into highly n‐doped AlGaAs. Detailed results on this and other structures are presented and implications for optimal design of heterostructure devices such as bipolar transistors are discussed.

Growth of SiC using hexamethyldisilane in a hydrogen‐poor ambient

Growth of cubic SiC has been carried out on Si(111), Si(100), and SiC(0001) substrates using chemical vapor deposition at atmospheric pressure. Hexamethyldisilane (HMDS) was used as the only precursor and pure Ar or a nonflammable mixture of Ar and H2 was used as the carrier gas. The crystallinity was characterized by x‐ray diffraction, reflection high energy electron diffraction (RHEED), and transmission electron microscopy. It was found that polycrystalline layers were obtained at low growth temperatures and with pure Ar as the carrier gas, while the crystallinity improved at temperatures above 1300 °C and when H2 was added. Under optimum growth conditions most of the grains are oriented with parallel epitaxy or with twinned epitaxy with respect to an (111) substrate. A Si/SiC heterodiode was also grown and it shows a breakdown voltage of more than 100 V.

Improved InP regrowth properties in metalorganic vapor phase epitaxy by addition of CCl4

Selective and planar regrowth of InP around stripe mesas up to 5.5 μm height formed with reactive ion etching in InP substrates has been made with metalorganic vapor phase epitaxy by adding CCl4 to the process gases. CCl4 seems to prevent nucleation on the phosphorous‐rich {111}B lattice planes and on the silicon‐nitride cap at the top of the mesa and hence permits reproducible regrowth with desired morphologies for integration of optoelectronic circuits at mesas oriented along the [110] direction. The addition of CCl4 does not influence dopant capability or the semi‐insulating properties of Fe‐doped material, for which a resistivity of 1×109 Ω cm has been obtained.