Si Epilayers Research Articles

Self-Sensing Micro- and Nanocantilevers with Attonewton-Scale Force Resolution

Thin, piezoresistive silicon cantilevers are shown to provide unprecedented sensitivity for force detection in an integrated, self-sensing, readily scalable configuration. The devices realized herein are patterned from single-crystal Si epilayer membranes utilizing bulk micro- and nanomachining processes. We demonstrate an electrically transduced force sensitivity of 235 aN/Hz1/2 at room temperature and 17 aN/Hz1/2 at 10 K. Enhancement of the p+ piezoresistive gauge factor is observed at cryogenic temperatures. The results are employed to elucidate the ultimate, low-temperature sensitivity attainable from self-sensing nanoelectromechanical systems utilizing displacement transduction based upon semiconducting piezoresistors.

Experimental measurements of majority and minority carrier lifetime profile in SI epilayers by the use of an improved OCVD method

In this letter, the first experimental results of a recently proposed technique for measuring the carrier lifetime profile are presented. The technique makes use of a four-terminal bipolar test structure to electrically define the epilayer volume where recombination occurs and employs the open circuit voltage decay method for lifetime parameters extraction. For the capability of the test structure to depurate measurements from the parasitic ohmic effects, the technique is able to measure the ambipolar and minority carrier lifetime along epilayer at high and low injection levels respectively. Comparisons of measurements with numerical simulations are reported to confirm the validity of the proposed technique.

Correction to "Characterization of Recombination Centers in Si Epilayers After Helium Implantation by Direct Measurement of Local Lifetime Distribution with the AC Lifetime Profiling Technique"

Correction to "Characterization of Recombination Centers in Si Epilayers After Helium Implantation by Direct Measurement of Local Lifetime Distribution with the AC Lifetime Profiling Technique"

Ｓｉ（００１）上ゲルマン吸着に伴う水素移動とＧｅ／Ｓｉ原子交換の観察

Germane (GeH4) adsorption at Si (001) at room temperature has been investigated through observations of surface hydrides by means of temperature-programmed desorption and multiple-internal-reflection Fourier-transformed infrared spectroscopy. For surfaces with considerable concentration of dimer vacancies, prepared by in-situ thermal cleaning followed by rapid cooling, saturation with germane presented almost full coverage of SiH without any Ge or Si-higher hydrides, which strongly suggests site exchange between ad-Ge and substrate Si atoms. For a smoother surface prepared by forming a Si epilayer, the Ge dihydride is much populated at higher doses of germane. From measurements using (1 × 2) single domain surface and polarized lights in FTIR, the Ge dihydrides are found to be at their “in-dimer” position rather than the “intra-row” position.

Dependence of GaAs:Si persistent photoconductivity on temperature and α-particle irradiation

We investigated the photoconductivity of GaAs:Si epilayer on SI-GaAs specimens. We measured the current from the time we switched on the illumination and after switching it off as a function of time at various temperatures from 250 to 330K. A small persistent photoconductivity starts to appear from 250K. At 330K a clear positive persistent photoconductivity (PPPC) appears. The persistent photoconductivity increases with temperature.Then the specimens were irradiated with α-particles from an Am241 source at 330K.A change in persistent photoconductivity is observed from the dose of 6×1012particles/cm2. At higher doses not only the current increases, but also the PPC duration. We try to explain these phenomena on the base of the existing theoretical models.

Kinetic formation and optical properties of self-assembled Ge/Si hut clusters

Structural and optical characterizations via reflection high-energy electron diffraction, atomic force microscopy and photoluminescence spectroscopy have been combined to investigate the kinetic formation of self-assembled Ge/Si hut clusters grown by ultra-high-vacuum chemical-vapor deposition. We show that point defects that are induced in the Ge and/or Si epilayers grown at low substrate temperatures greatly influence the optical properties of Ge/Si hut clusters. By undertaking controlled annealing experiments, in particular by rapid annealing up to a temperature of 900 °C for a very short period of time, we show that it is possible to ‘repair’ those defects, giving rise to the observation of the proper photoluminescence of hut clusters while Ge/Si intermixing is minimized.

Direct growth of CdTe(1 0 0) epilayers on Si(1 0 0) substrate by hot wall epitaxy

Strong preferential (1 0 0) orientation is observed for the first time in the CdTe thin films directly grown on Si(1 0 0) substrates without any buffer layers. This result is attributed to the fact that the epilayer is grown directly on the hydrogen-terminated Si substrate without any preheating treatment. The crystal qualities of CdTe(1 0 0)/Si(1 0 0) and CdTe(1 1 1)/Si(1 1 1) epilayers obtained at the same growth conditions were compared. Atomic force microscopy observations reveal different surface morphology at the early stages of the crystal growth for CdTe(1 1 1)/Si(1 1 1) and CdTe(1 0 0)/Si(1 0 0) epilayers, implying that they are governed by different growth mechanisms. The nucleation of CdTe(1 0 0)/Si(1 0 0) starts with 3D islands having a dome shape. It is demonstrated that the height and diameter distributions narrow and the aspect ratio decreases with decreasing the growth time. The crystallinity of CdTe(1 0 0)/Si(1 0 0) epilayers is inferior to that of CdTe(1 1 1)/Si(1 1 1) due to a double-domain structure.

Characterization of Recombination Centers in Si Epilayers After He Implantation by Direct Measurement of Local Lifetime Distribution With the AC Lifetime Profiling Technique

The distribution of recombination centers induced in Si epi-substrates by helium (He) implantation is obtained for the first time by direct measurement of local recombination lifetime profile along the layer, using the ac differential lifetime profiling technique. The different energy levels of the recombination centers induced by He implantation at different doses and energies have been extracted, as a function of the position in the layer, by temperature scanning of the lifetime profiles. The lifetime measurements clearly demonstrate the presence of a secondary defect distribution that extend from the region of maximum primary damage both at lower and higher depths respect to the stopping range depth, due to the relatively large concentration of primary defects created near the stopping range, and give a coherent picture of the effects of He implant on the "local" lifetime.

アークプラズマガンを用いた新規材料ＧｅＣ薄膜の分子線エピタキシー成長

Novel GeC epilayers on Si (001) substrates were grown by using a molecular beam epitaxy (MBE) with a vacuum arc plasma gun as a new-type C source for a first time. To improve crystallinity and obtain a higher substitutional C content x in the Ge1-xCx epilayers, dependence of the growth mode and C incorporation upon the supplied C fraction and growth temperature was investigated systematically by reflection high-energy electron diffraction, X-ray diffraction and Raman spectroscopy analyses. Further, an effect of Ar+ ion irradiation on substitutional C incorporation into the MBE-grown GeC /Si (001) epilayers was clarified. As the result, the maximum value of x= 2.9% was obtained in a singlecrystalline structure. From measuring the optical absorption spectra with FT-IR, it was found out that the Get1-xCx/Si (001) epilayers with 0≤x≤2.0% have an indirect transition-type band structure and a very large bandgap bowing parameter b= 13.4 eV.

Twin suppression in HWE grown CdTe epilayers on Si(111) by novel two-step growth procedure

The crystal quality of CdTe(111)/Si(111) epilayers grown by hot wall epitaxy (HWE) is investigated by symmetric and asymmetric high resolution X-ray diffraction (HRXRD) to reveal the main reason for the improved crystallinity when applying originally designed two-step growth method. HRXRD data show that the two-step growth method reduces twin content remarkably compared to the conventional one-step growth. The twin content in CdTe epilayer is extremely sensitive to the growth conditions, especially to the growth rate at the early stage of the crystal growth. The direct growth of high quality CdTe epilayer on Si(111) must be a promising substrate for fabricating high performance MCT infrared detectors.

Surfactant enhanced growth of thin Si films on CaF 2/Si(1 1 1)

MBE growth of Si thin films on CaF 2/Si(1 1 1) has been studied by various growth techniques with and without surfactant. In both cases high temperature depositions results in a growth of 3D Si clusters and a large discrepancy between the nominally evaporated and the actually deposited amount of Si on the CaF 2 surface. Without surfactant, the deposition at room temperature with a subsequent annealing steps improved the quality of the Si epilayers but was accompanied by the formation of holes and trenches in the Si film. A surfactant-modified epitaxy method, where the room temperature Si deposition was followed by annealing under a flux of the surfactant Sb, resulted in continuous, smooth and epitaxial crystalline Si film on CaF 2, with a sharp ( 3 x 3 )R30° reconstruction. Although the microcrystalline structure is not yet perfect the quality of the layers is much better than that of all films prepared by the other employed growth processes.

Comparison of the ion induced charge collection in Si epilayer and SOI devices

It is known that the single-event phenomena (SEP) are the malfunction of micro electronics devices caused by the impact of an energetic heavy ion. Improving the tolerance of devices to the SEP requires a better understanding of basic charge collection mechanisms on the timescales of the order of picoseconds. In order to better elucidate these mechanisms, we measure the fast transient current resulting from heavy ion strikes with a fast sampling data collection system and a heavy ion microbeam line at JAERI. In this paper we report on differences in both the transient current and charge collection from 15 MeV carbon ions on silicon-on-insulator, Si epilayer and bulk p +n junction diodes and charge transportation under MeV ion injection is discussed.

TCAD modeling of single MeV ion induced charge collection processes in Si devices

Single MeV ion induced currents are directly responsible for a wide range of single event phenomena leading to temporary or permanent malfunction of devices in radiation environments such as space. The active regions of a device act as a source of transient currents injected into a device subsystem by collecting the charge induced by MeV ions. As such, the charge collection process is an important step in understanding mechanisms that lead to device malfunction. In this paper, we present transient current data collected on Si epilayer devices with 15 MeV O 4+ ions focused using a MeV heavy ion micro-probe. The measured transient currents are compared to quasi-3D simulation using ISE TCAD software. Critical factors influencing the fidelity of the measurement technique and modeling of heavy ion track models are also discussed.

DOPING AND GROWTH OF THIN Si EPILAYER AND SiGe BY UHV/CVD

The real time B-doped thin Si and SiGe epilayers on diameter 3-inch Si substrates were grown by an ultrahigh vacuum chemical vapor deposition (UHV/CVD) system. The substrate temperature during growth was from 550 ~ 780°C. The properties of the epilayers were characterized by secondary ion mass spectrum (SIMS), Fourier transform infrared spectroscopy (FTIR), spreading resistance profile (SRP) and double crystal x-ray diffraction (DCXRD). The carrier concentration in the intrinsic Si epilayer was about 1012 cm -3 and the resistivity was as high as about 10000 Ωcm. In addition, the abrupt transition and B-doped concentration of 1015 ~ 1019 cm -3 were achieved for Si and SiGe epilayers.

Hydrogenation effect on silicon on sapphire grown by rapid thermal chemical vapor deposition

Single crystalline Si epilayers were grown on sapphire (1 1 ̄ 0 2) substrates through a three-step growth method by rapid thermal chemical vapor deposition (RTCVD). Hydrogenation of the epilayers was performed by the hydrogen-plasma exposure (HPE) in a remote plasma chemical vapor deposition (RPCVD) system, following rapid thermal annealing. It was found that the hydrogenation treatment improves the crystallinity of the Si epilayer as well as the electrical properties of Si epilayers. After hydrogenation, especially, the intensity of the deep level defects which are responsible for the lattice mismatch between Si and the sapphire substrate decreases. Also, dislocations and microtwins are reduced remarkably, improving the crystallinity. In Schottky diodes fabricated on hydrogenation-processed Si epilayers, the leakage current decreases one order of magnitude in comparison to non-hydrogenated samples. It is suggested that these characteristics could be explained by the hydrogen incorporation at defects.

Optical properties of self-assembled Ge wires grown on Si(113)

We report photoluminescence and Raman scattering measurements of Ge wires formed by self-assembly on Si(113) substrates. The samples were grown at a growth temperature of 500 °C on Si(113) substrates by solid-source molecular-beam epitaxy. Atomic force microscopy results clearly show the formation of coherent wire-shaped islands elongated in the [33-2] direction, some with lengths exceeding 500 nm. Micro-Raman measurements indicate that at this low growth temperature intermixing of the silicon and germanium is restricted with an average Ge fraction exceeding 0.7. Capping of the wires with a 20 nm Si epilayer enables the observation of low-temperature photoluminescence. A series of samples with increasing Ge coverage were studied and the onset of Ge islanding is observed to occur at a coverage of 5 monolayers. Wire formation occurs at coverages of 6 monolayers or greater. The observed emission band from the wires has a line shape quite different from that observed from Ge islands on Si[100], being substantially narrower in energy. A stochastic calculation based on idealized quantum wires is presented which reproduces the observed photoluminescence line shape well.

Temperature dependence of heavy ion-induced current transients in Si epilayer devices

We report on the temperature dependence of the heavy-ion transient-ion beam induced current response of Si epilayer devices from 80 to 300 K. The measurements were performed on a heavy-ion microbeam in conjunction with the new transient-ion beam induced current system developed at the Japan Atomic Energy Research Institute. Furthermore, we perform a detailed comparison with technology computer-aided design (TCAD) simulations and discuss the results in terms of TCAD modeling, experimental procedure, and the implications for temperature-related single-event upset modeling.

Awards

The Awards Committee selected 11 papers from the oral and poster presentations at the 2001 RADECS Conference as candidates for Outstanding Paper. The second step of the evaluation process, rating the final manuscripts, permitted the selection of the best one from those 11 top papers. In addition to the Outstanding Paper Award, one Meritorious Paper was selected. The results are as follows: Outstanding Paper: "Characterization of the Parasitic Bipolar Amplification in SOI Technologies Submitted to Transient Irradiation" by V. Ferlet-Cavrois, C. Marcandella, G. Giraud, G. Gasiot, T. Colladant, O. Musseau,C. Fenouillet, and J. du Port de Poncharra. Meritorious Paper: "Temperature Dependence of Heavy Ion Induced Current Transients in Si Epilayer Devices" by J.S. Laird, T. Hirao, S. Onoda, H. Mori, and H. Itoh.

Effect of Si doping on the growth and microstructure of GaN grown on Si(1 1 1) using SiC as a buffer layer

We studied the initial growth of Si-doped GaN (GaN:Si) epilayers grown under both N- and Ga-rich conditions. Upon Si doping, the surface polarity changed from N- to Ga-polarity. The surface diffusion kinetics of the Ga adatoms of the GaN:Si epilayers depended strongly on the Ga/N flux ratio. GaN:Si films with good crystal quality were obtained for a Ga/N flux ratio slightly larger than 1. The dislocation density decreased about one order of magnitude, while the stacking fault and cubic phase density near the interfacial region increased. The main types of dislocations in the undoped GaN were mixed and edge dislocations. In the GaN:Si, the main dislocations were pure-edge dislocations. The dislocation-density reduction in the GaN:Si may have been due to a low density of mixed dislocations in the presence of a high density of stacking faults and cubic phase.

Non-destructive characterisation of doped Si and SiGe epilayers using FTIR spectroscopic ellipsometry (FTIR-SE)

FTIR-SE has been used to determine, non-destructively, carrier density ( n, p) and thickness ( t) of Si and SiGe epitaxial layers. The FTIR-SE measurements were made using a SOPRA GES5-FTIR instrument, operating over the range 600–4000 cm −1. A range of samples has been studied, including undoped and doped Si epilayers with t ≈1–17 μm, p ≈7×10 17–1.5×10 19 cm −3 and doped Si 0.9Ge 0.1 epilayers with t ≈50–100 nm, p ≈1–3×10 19 cm −3. The results were compared with SIMS and four-point probe measurements. For the Si epilayers, excellent agreement was obtained for thickness values and best agreement for carrier density values was obtained using m *=0.26 m e in the Drude free-carrier analysis. Carrier density of thin SiGe layers has been measured by FTIR-SE for the first time. A novel layer structure was used to improve sensitivity in the available spectral range. Lower limits of sensitivity to thickness and doping level have been established. Both thickness and carrier density were determined with good precision for 100 nm layers.