Atsushi Kurobe

High performance strained-Si p-MOSFETs on SiGe-on-insulator substrates fabricated by SIMOX technology

We have proposed a new MOSFET structure, strained-Si/Si/sub 0.9/Ge/sub 0.1/-on-Insulator (SSGOI) MOSFETs applicable to the sub-100 nm generation. This SSGOI structure was successfully fabricated by the combination of SIMOX technology and the Si re-growth technique. The strained-Si in SSGOI was found to have good crystal quality and very flat interfaces. SSGOI p-MOSFETs exhibited good FET characteristics. It was demonstrated, for the first time, that the hole mobility of the SSGOI p-MOSFETs is higher that of the universal mobility of conventional Si p-MOSFETs.

Correlation Effects on Variable Range Hopping Conduction and the Magnetoresistance

Effects of intra-state correlation on the variable range hopping are investigated in the absence and presence of a magnetic field. In the absence of a magnetic field, Motts expression for the resistivity, ρ∝exp [ T 0 / T ] 1/4 , still holds in its temperature dependence. However, the prefactor T 0 now depends on two types of localization lengths brought about by the intra-state correlation. Magnetoresistance is found to be positive due to the intra-state correlation. It shows a linear dependence on a magnetic field in lower magnetic fields and saturates above a certain magnetic field.

Effects of well number, cavity length, and facet reflectivity on the reduction of threshold current of GaAs/AlGaAs multiquantum well lasers

The optimum design for reducing the threshold current of GaAs/AlGaAs multiquantum well lasers is determined experimentally. The lowest threshold current density is realized by using single and multiquantum wells at long and short cavity lengths, respectively. The threshold current has a minimum at the optimum cavity length: the minimum threshold current is smaller for a larger number of quantum wells, and the optimum cavity length is inversely proportional to the number of wells. Experiments are compared to the theory developed by P.W.A. McIlroy, et al. (ibid., vol.21, no.12, p.1958-63, 1985) and limiting performances of quantum well lasers with various numbers of wells are presented. The reduction of the threshold current by high reflectivity coatings is also demonstrated, and a threshold current as low as 1.86 mA at 15 degrees C is reported. >

Advanced SOI p-MOSFETs with strained-Si channel on SiGe-on-insulator substrate fabricated by SIMOX technology

We have newly developed an advanced SOI p-MOSFET with strained-Si channel on insulator (strained-SOI) structure fabricated by SIMOX (separation-by-implanted-oxygen) technology. The characteristics of this strained-SOI substrate and electrical properties of strained-SOI MOSFETs have been experimentally studied. Using strained-Si/relaxed-SiGe epitaxy technology and usual SIMOX process, we have successfully formed the layered structure of fully-strained-Si (20 nm)/fully-relaxed-SiGe film (290 nm) on uniform buried oxide layer (85 nm) inside SiGe layer. Good drain current characteristics have been obtained in strained-SOI MOSFETs. It is found that the hole mobility is enhanced in strained-SOI p-MOSFETs, compared to the universal hole mobility in an inversion layer and the mobility of control SOI p-MOSFETs. The enhancement of the drive current has been kept constant down to 0.3 /spl mu/m of the effective channel length.

Device structure and electrical characteristics of strained-Si-on-insulator (strained-SOI) MOSFETs

Strained-Si CMOS is an attractive device structure to be able to relax several fundamental limitations of CMOS scaling, because of high electron and hole mobility and compatibility with Si CMOS standard processing. In this paper, we present a new device structure including strained-Si channel, strained-SOI MOSFET, applicable to CMOS under sub-100 nm technology nodes. The main feature of this device is that thin strained-Si channel/relaxed SiGe heterostructures are formed on buried oxides. The principle and the advantages are described in detail. The strained-SOI structure has been successfully fabricated by combining the SIMOX technology with regrowth of strained Si films. It is demonstrated that strained-SOI n- and p-channel MOSFETs have mobilities 1.6 and 1.3 times higher than conventional Si MOSFETs, respectively. We also present a novel technique for fabricating ultra-thin SiGe-on-insulator (SGOI) virtual substrates with high Ge content by high temperature oxidation of SGOI with lower Ge content. A 16-nm-SGOI substrate having a Ge content as high as 57% has been successfully fabricated.

Formation of strained-silicon layer on thin relaxed-SiGe/SiO2/Si structure using SIMOX technology

Abstract The fabrication of a 20 nm strained-Si on a 360 nm relaxed-SiGe layer structure using SIMOX technology was successfully demonstrated for the first time. The thin relaxed-SiGe layer on SiO2 was obtained by the direct implantation of oxygen into the thick SiGe layer, and by annealing. It was found that hydrogen termination produced by HF treatment allows successful regrowth of strained-Si layer on the thin relaxed-SiGe layer by ultra-high vacuum chemical vapor deposition (UHV-CVD). Structure analyses such as secondary ion mass spectroscopy (SIMS), Rutherford back-scattering spectroscopy (RBS) analysis, and cross-sectional transmitting electron microscopic (TEM) revealed the perfection of the layer structure of Si/SiGe/SiO2. The fully strained-Si on the relaxed-SiGe layers was also confirmed by Raman spectroscopy. It was revealed that the combination of the SIMOX process and the regrowth on the SiGe layer provides an advanced layer structure including this strained-Si for future novel devices.

The effect of conduction band non-parabolicity on inter-sub-band absorption in doped quantum wells

The authors have theoretically treated the effect of conduction band non-parabolicity on inter-sub-band absorption in doped semiconductor quantum wells. The authors have derived an analytical expression for the absorption at zero temperature. The absorption peak is shifted to lower energies and the peak height is reduced by non-parabolicity. These effects are small for GaAs-based quantum wells, but may be detrimental to InGaAs quantum wells.

Possibility of optical bistability due to resonant intersubband excitation in stepped modulation‐doped quantum wells

We propose the use of a novel doped, stepped semiconductor quantum well structure as an optical nonlinear element. The large nonlinearity results from the change of many‐body effects on resonant excitation of electrons from the ground to the first excited subband. Self‐consistent calculations showed that the intersubband energy separation can be increased by up to 7 meV on intense illumination, compared to 1 meV for a conventional, square quantum well. We estimate that optical switching at powers below 1 W are feasible in an optimized structure, with switching times of about 1 ps.

FABRICATION OF HIGH MOBILITY IN SITU BACK-GATED (311)A HOLE GAS HETEROJUNCTIONS

Using an n-type (311)A GaAs substrate we have fabricated in situ back-gated GaAs/(Al,Ga)As hole gases with mobilities of μ=1.1×106 cm2 V−1 s−1 at 30 mK. We have investigated both experimentally and theoretically the scattering mechanisms that limit the mobility in both the [233] and [011] directions. Using a combination of front and back gates to keep the carrier density constant, we can distinguish between scattering mechanisms which are primarily dependent on the carrier density and those that are sensitive to the shape of the hole wave function. This approach also eliminates complications arising from the variations of the Fermi surface anisotropy with carrier density. Our data confirms that anisotropic interface roughness scattering, arising from the nature of the (311)A GaAs surface, is the dominant scattering mechanism at carrier densities down to ps=5.0×1010 cm−2.

Experimental evidence of valence band deformation due to strain in inverted hole channel of strained-Si pMOSFETs

We found experimental evidence for the first time that the in-plane strain affects the anisotropy of the hole subbands in the strained-Si pMOSFETs. The anisotropy was characterized by Hall factor, which was obtained by combining Hall and capacitance-voltage measurements. It was confirmed by Raman spectroscopy that the value of the strain in the strained-Si layer becomes larger with increasing Ge content x in the Si12xGex buffer layer. At low temperature, Hall factors for xa 0:11, 0.14 and 0.19 devices exhibit almost the same values, which are larger than the values for the unstrained Si-pMOSFET. From the result, the lowest subband in the strained-Si device was found to be more isotropic than that in the unstrained-Si device. As temperature is raised up to 180 K, the Hall factor is almost constant for xa 0:19 device, whereas it decreases gradually for xa 0:11 device. The temperature dependence indicates that the lowest subband in the strained-Si device is more isotropic than the second subband. These results suggest that the lowest and the second subbands originate in the light- and the heavyhole bands, respectively. This assignment is consistent with a recent calculation on two-dimensional hole gas in strained-Si pMOSFETs. q 2000 Elsevier Science S.A. All rights reserved.