Svetlana Beljakowa

Recombination activity of interstitial chromium and chromium-boron pairs in silicon

The recombination activity of interstitial chromium (Cri) and pairs of interstitial chromium and substitutional boron (CriBs) in crystalline silicon is studied by combining temperature- and injection-dependent lifetime and deep-level transient spectroscopy measurements on intentionally chromium-contaminated n- and p-type silicon wafers. Cri as well as CriBs pairs are found to be one order of magnitude less recombination active than widely assumed. In the case of Cri, a defect energy level of EC−Et=0.24 eV, an electron capture cross section of σn=2×10−14 cm2, and a hole capture cross section of σp=4×10−15 cm2 are determined. For CriBs pairs, measurements on boron-doped p-type silicon result in Et−EV=0.28 eV, σn=5×10−15 cm2, and σp=1×10−14 cm2. Theoretical calculations using the Shockley–Read–Hall theory show that it depends crucially on the doping concentration whether Cri or CriBs is the more active recombination center. Using a calibration function calculated from the defect parameters determined in this...

Determining the defect parameters of the deep aluminum-related defect center in silicon

Through a combined application of two characterization methods, deep-level transient spectroscopy and lifetime spectroscopy, the lifetime-limiting defect level in intentionally aluminum-contaminated Czochralski silicon has been analyzed and a complete set of defect parameters could be obtained. This aluminum-related defect center is found to be located at an energy level of Et−EV=0.44±0.02eV and exhibits an asymmetric capture cross section, with σp=3.6×10−13cm2 and σn=3.1×10−10cm2 being the hole and electron capture cross sections, respectively. The investigated defect center is attributed to the aluminum-oxygen complex (Al–O).

Electronic properties and dopant pairing behavior of manganese in boron-doped silicon

One of the authors T.R. gratefully acknowledges a scholarship of the German Federal Environmental Foundation Deutsche Bundesstiftung Umwelt. Another D.M. is supported by an Australian Research Council QEII Fellowship.

Control of the Flatband Voltage of 4H-SiC Metal-Oxide Semiconductor (MOS) Capacitors by Co-Implantation of Nitrogen and Aluminum

In n-type 4H-SiC, over-oxidation of an implanted surface-near, Gaussian nitrogen-profile results in MOS capacitors, which possess a distinctly reduced density of interface states Dit and an undesirable large negative flatband voltage UFB. Their values are determined by the implantation parameters and the thickness of the oxide layer. The negative flatband voltage can strongly be compensated in the case that a Gaussian aluminum-profile is co-implanted prior to the oxidation. Depending on the conditions of the Al implantation, UFB can be controlled within a wide range. Secondary ion mass spectrometry analyses reveal that the implanted N and Al atoms are mobile in the oxide layer during the oxidation process and are partly accumulated at the SiC/SiO2 interface.

Detection and Electrical Characterization of Defects at the SiO2/4H-SiC Interface

Two electrical measurement techniques are frequently employed for the characteri- zation of traps at the SiO2/SiC interface: the thermal dielectric relaxation current (TDRC) and the conductance method (CM). When plotting Dit as a function of the energy position Eit in the bandgap both techniques reveal comparable results for deep interface traps (ECEit > 0:3 eV). For shallower traps, CM always shows a strong increase of Dit which originates from near interface traps (NIT). TDRC provides a contradictory result, namely a slight decrease of Dit. In this paper, we show that the position of NITs in the oxide close to the interface is responsible for the invisibility of these traps in TDRC spectra. We further show that NITs become detectable by the TDRC method by using a discharging voltage Vdis close to the accumulation regime. However, due to the Shockley-Ramo-Theorem the contribution of NITs to the Dit in TDRC spectra is strongly suppressed and can be increased by using thin oxides.

Iron-Related Defect Centers in 4H-SiC Detected by Deep Level Transient Spectroscopy

Fe-implanted n-/p-type 4H-SiC samples were investigated by deep level transient spectroscopy (DLTS). In order to be able to separate Fe-related defect centers from defects caused by implantation damage, a corresponding Ar-profile was implanted. No Fe-related defects were observed in n-type 4H-SiC, while two Fe-related centers could be identified in p-type 4H-SiC. The electrical behavior of these centers is donor-like.

Thermal Stability of Defect Centers in n- and p-Type 4H-SiC Epilayers Generated by Irradiation with High-Energy Electrons

This paper comprises a systematic study of the thermal stability of defect centers observed in n- and p-type 4H-SiC by deep level transient spectroscopy (DLTS); the defects are generated by irradiation with high-energy electrons of 170 keV or 1 MeV.

Preannealing Effect on Mobility of N-/Al-Coimplanted and Over-Oxidized 4H-SiC MOSFETs

The authors investigated the effect of preannealing on N-/Al-coimplanted and over-oxidized Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs). The preannealing process causes a decrease of the Hall mobility and the effective mobility, and an increase of the interface state density. Secondary ion mass spectroscopy (SIMS) measurements revealed that the N concentration at the SiO2/SiC interface in preannealed samples is lower than in not-preannealed samples, which might be the reason for in the increase of the interface state density. In MOSFETs without preannealing, more N atoms are piled up at the SiO2/SiC interface, leading to the lower interface state density and higher mobility.

Effect of germanium doping on electrical properties of n-type 4H-SiC homoepitaxial layers grown by chemical vapor deposition

The effect of germanium (Ge) on n-type 4H-SiC is experimentally studied by electrical characterization of homoepitaxial layers grown by chemical vapor deposition (CVD). Measurements show that electrical properties of epitaxial layers can be changed by intentional incorporation of germane (GeH4) gas during the deposition process. On the nanoscale, two-dimensional mappings acquired with conductive atomic force microscopy show preferential conductive paths on the surface of Ge-doped samples, which are related to the presence of this isoelectronic impurity. Hall effect measurements confirm that also macroscopic electrical properties of n-type 4H-SiC are improved due to incorporation of Ge into SiC during CVD growth. In particular, despite equal free electron concentration, enhanced mobility in a wide temperature range is measured in Ge-doped samples as compared to a pure 4H-SiC layer. Based on our results from Hall effect measurements as well as admittance spectroscopy and deep level transient spectroscopy, i...

Characterization of Ge-Doped Homoepitaxial Layers Grown by Chemical Vapor Deposition

We have investigated the electrical properties of n-type 4H-SiC in-situ germanium-doped homoepitaxial layers grown by chemical vapor deposition. Germanium is an isoelectronic impurity and, therefore, not expected to contribute to the conductivity. However, Hall effect measurements taken on samples with and without germanium revealed an enhanced mobility by a factor of ≈2 at T ≈ 55 K in the germanium-doped sample despite equal free electron concentration and equal compensation. Deep level transient spectroscopy (DLTS) measurements taken on germanium-doped samples reveal negative peaks indicating the presence of charged extended defects.