Papers by Author: Massimo Camarda

Abstract: In this paper we have studied the connection between crystal quality and electrical transport in 4H-SiC by simultaneous micro-photoluminescence (μPL) and micro-photocurrent (μPC) measurements. We have used a focused HeCd laser at 325nm (i.e. above bandgap) to measure with a spatial resolution of few microns both the μPL spectra and the I-V characteristics in 4H-SiC/NiSi Schottky diodes. We found that extended defects exhibiting a photoluminescence peak located at 2.9eV (i.e single Shockley or bar shaped stacking faults) can produce an increase of the measured PC whereas other defects, such as the (4,4) stacking fault, can be considered as ‘killer defects’, strongly reducing the photocurrent.

Abstract: In this paper we use three dimensional kinetic Monte Carlo simulations on super-lattices to study the hetero-polytypical growth of cubic silicon carbide polytype (3C-SiC) on hexagonal 6H-SiC step-bunched substrates with miscuts towards the <11-20> and <1-100> directions. We find that the preferential 3C conversion observed on <1-100> misoriented substrates could be due to a different step-to-island interaction which enhances island stability and expansion in this specific direction. For this reason 3-4° degrees off step-bunched 6H substrates with miscut towards the <1-100> direction should be the best choice for the stable and reproducible hetero-polytypical growth of high quality cubic epitaxial films.

Abstract: Recently, a new Micro-Raman technique has been used to detect extended defects in 4H-SiC homoepitaxy. The method is based on the local increase of free carriers in undoped epitaxies (n < 10¹⁶ at/cm^-3) produced by a high power laser. The Longitudinal optical Raman mode (LO) is coupled with the electronic plasma generated by the laser pumping; such a Raman signal is sensitive to crystallographic defects that lead to trapping (or dispersion) of the free carriers which results in a loss of coupling. The monitoring of the LOPC allows determining the spatial morphology of extended defects. The results show that the detection of defects via the induced-LOPC (i-LOPC) is totally independent from the stacking fault photoluminescence signals that cover a large energy range up to 0,7eV thus allowing for a single-scan simultaneous determination of any kind of stacking fault. Also, the i-LOPC method shows the connection between the carrier concentration and the carrier lifetime for undoped film, obtaining meaningful information related to electrical properties of the film, and demonstrating that this technique is a fast, reliable and powerful method to characterize most of crystallographic defects (extended and point-like defects) in the semiconductor field.

Abstract: The design, fabrication, early testing and material property assessment work related to the development of an opto-mechanical pressure sensor implemented with hetero-epitaxial 3C-SiC on silicon is described. The sensor is constituted by a single-crystal 3C-SiC membrane whose deflection upon pressure application is measured using a fiber-optic interferometric readout. The fabrication of sensor prototypes and micromachined 3C-SiC membranes for test purposes is described and the results of bulge tests on the membranes are reported. Functional characterization of the sensor prototypes in the pressure range 0-3 bar is also presented, showing good linearity and reproducibility of the sensor response, sensitivity of roughly 2 mV/bar and estimated pressure resolution around 0.5 bar on a 0-200 bar dynamic range.

Abstract: The following paper explores the development the bulge test technique combined with the micro-Raman analysis and a refined load-deflection model for high quality 3C-SiC squared-membranes. By the minimization of the total elastic energy, starting from the isotropic relation between the stress tensor and the strain tensor, it is possible to calculate the relationship between the maximum deflection and the applied pressure, in both regime of small and large deflection. From the measured breaking pressure through the refined model it is possible to evaluate the breaking strain of the membrane. Furthermore, the relationship between the measured shift of Raman Transverse Optical (TO) phonon modes and the total residual strain (Δa/a) within the epitaxial 3C-SiC layer was found.

Abstract: Micro Raman characterization has been used to determine the stress status of 3C-SiC epilayer grown on pseudomorphic-Si thin layer on Si_1-xGe_x/Si(001). The strain conditions of the Si_1-xGe_x films grown on Si(001) have been determined by the analysis of additional Silicon Raman peaks, which Raman shifts are related to the lattice parameter. Through the analysis of the Raman spectra, the correlation between the Si_1-xGe_x film, the crystal quality and the stress relaxation of the 3C-SiC as a function of the Germanium fraction (x), have been evaluated. The increase of Germanium fraction determines the reduction of the voids density located at the 3C-SiC/Si interface and the relaxation of the stress within the epilayer. Moreover, the 3C-SiC crystal quality, monitored by the Full Width at Half Maximum of the TO Raman mode, remains unchanged for any Germanium fraction values.

Abstract: In this paper we used three dimensional kinetic Monte Carlo simulations on super-lattices to study the hetero-polytypical growth of cubic silicon carbide polytype (3C-SiC) on hexagonal 6H-SiC substrates with miscuts towards the <11-20> and <1-100> directions. We analyze the grown film for different miscut angles (in the range 2° to 12° degrees) and different growth rates, finding that substrates with miscut of 3-4° degrees towards the <1-100> direction should be the best choice for the growth of high quality cubic epitaxial films, being able to promote, given a suitable pre-growth treatment to induce step bunching, the nucleation of single domain 3C-SiC films.

Abstract: In this paper we investigate the role of the growth rate (varied by changing the Si/H₂ ratio and using TCS to avoid Si droplet formation) on the surface roughness (R_q), the density of single Shockley stacking faults (SSSF) and 3C-inclusions (i.e. epi-stacking faults, ESF). We find that optimized processes with higher growth rates allow to improve the films in all the considered aspects. This result, together with the reduced cost of growth processes, indicates that high growth rates should always be used to improve the overall quality of 4H-SiC homoepitaxial growths. Furthermore we analyze the connection between surface morphology and density of traps (D_it) at the SiO₂/SiC interface in fabricated MOS devices finding consistent indications that higher surface roughness (step-bunched surfaces) can improve the quality of the interface by reducing the D_it value.

Abstract: Preliminary results of 150mm SiC 4H 4°off have been obtained with the new 150mm automatic horizontal hot wall reactor PE1O6, using chlorinated chemistry (SiHCl₃ + C₂H₄). A new injection system has been tested in two configurations and results will be shown in this paper. AFM surface roughness measurements and epi defect density have been reported.

Abstract: Micro-Raman characterization has been used as alternative technique to the photoluminescence in order to detect and study 4H-SiC stacking faults. The alteration of the crystalline stacking sequence perturbs the phonon-plasmon coupling which acts between the crystalline phonon modes and the electronic plasma, due to the doping element (N). The shape and the symmetry of the Longitudinal optical Raman mode is strongly correlated to the doping level of the material thus, through the monitoring of the Raman mode, the spatial morphology of the defect can be completely recovered and compared to the results provided by photoluminescence technique. The results show that such a technique allows a very fast inspection on large wafer, because it is totally independent of the stacking fault photoluminescence signals, which cover a large energy range, up to 0.7 eV.