C. Rosenblad

High hole mobility in Si0.17Ge0.83 channel metal–oxide–semiconductor field-effect transistors grown by plasma-enhanced chemical vapor deposition

We report on effective hole mobility in SiGe-based metal–oxide–semiconductor (MOS) field-effect transistors grown by low-energy plasma-enhanced chemical vapor deposition. The heterostructure layer stack consists of a strained Si0.17Ge0.83 alloy channel on a thick compositionally-graded Si0.52Ge0.48 buffer. Structural assessment was done by high resolution x-ray diffraction. Maximum effective hole mobilities of 760 and 4400 cm2/Vs have been measured at 300 and 77 K, respectively. These values exceed the hole mobility in a conventional Si p-MOS device by a factor of 4 and reach the mobility data of conventional Si n-MOS transistors.

SILICON EPITAXY BY LOW-ENERGY PLASMA ENHANCED CHEMICAL VAPOR DEPOSITION

A new technique for semiconductor epitaxy at low substrate temperatures is presented, called low-energy dc plasma enhanced chemical vapor deposition. The method has been applied to Si homoepitaxy at substrate temperatures between 400 and 600 °C and growth rates between 0.1 and 1 nm/s, using silane as the reactive gas. The quality of the Si films has been examined by reflection high-energy electron diffraction, scanning tunneling microscopy, cross-section transmission electron microscopy, and high-resolution x-ray diffraction. Two effects have been identified to lead to the formation of stacking faults after an initial layer of defect-free growth: (1) substrate bombardment by ions with energies in excess of 15 eV, and (2) hydrogen adsorption limiting the surface mobility of Si atoms and silane radicals. Both result in the accumulation of surface roughness, facilitating the nucleation of stacking faults when the roughness reaches a critical level. Defect introduction can be eliminated effectively by biasing...

A plasma process for ultrafast deposition of SiGe graded buffer layers

Low energy plasma enhanced chemical vapor deposition (LEPECVD) has been applied to the synthesis of Si-modulation doped field effect transistor structures, comprising a SiGe relaxed buffer layer and a modulation doped strained Si channel. A growth rate of at least 5 nm/s for the relaxed SiGe buffer layer is well above that obtainable by any other technique. Due to the low ion energies involved in LEPECVD, ion damage is absent, despite a huge plasma density. The structural quality of the LEPECVD grown SiGe buffer layers is comparable to that of state-of-the-art material. The electronic properties of the material were evaluated by growing modulation doped Si quantum wells on the buffer layers. We obtain a low temperature (2 K) Hall mobility of μH=2.5×104 cm2/Vs for the electrons in the Si channel at an electron sheet density of ns=8.6×1011 cm−2.

Alternatives to thick MBE-grown relaxed SiGe buffers

Abstract We have investigated several growth concepts for strain relieved SiGe buffers as basis for high frequency transistors. Modulation doped quantum wells (MODQWs) were realized by molecular beam epitaxy (MBE) on top of thick graded buffers prepared by MBE, ultra-high vacuum chemical vapor deposition (UHVCVD) and low-energy plasma-enhanced CVD (LEPECVD). Additionally, thin buffers including a specific layer grown at low temperature (LT) were realized entirely by MBE. The overgrown thick CVD samples show comparable transport properties and thermal stabilities to those on thick graded MBE buffers. Mobilities of up to 90 000 cm 2 /V s have been measured at 30 K. Thin LT-MBE structures show slightly worse properties but are superior to conventional constant composition buffers.

Fabrication and modeling of gigahertz photodetectors in heteroepitaxial Ge-on-Si using a graded buffer layer deposited by low energy plasma enhanced CVD

Photodetectors were fabricated in a heteroepitaxial Ge-on-Si deposited by low energy plasma enhanced CVD. Dark current density of 4.6 nA//spl mu/m, 49 % quantum efficiency, and a -3 dB bandwidth of 3.5 GHz were measured at 1.3 /spl mu/m wavelength and -3 V bias. Numerical simulations predict device modifications can achieve 10 Gbps (/spl cong/ 7 GHz) bandwidth.

Strain relaxation of graded SiGe buffers grown at very high rates

Abstract The strain relaxation in compositionally graded SiGe alloy buffers was studied as a function of growth temperature and growth rate. We have used a plasma enhanced CVD technique that we call low energy plasma enhanced chemical vapour deposition (LEPECVD) to access growth rates in the range of 0.9–3.8 nm/s at substrate temperatures between 640 and 725°C. The samples were analysed by X-ray reciprocal space mapping, transmission electron microscopy and defect etching. Despite the very high growth rate, the structural properties of the buffers are identical to buffers grown at rates one or two orders of magnitude lower. The threading dislocation density is shown to decrease significantly with increasing temperature in the investigated range.

Virtual substrates for the n- and p-type Si-MODFET grown at very high rates

Low-energy plasma-enhanced chemical vapour deposition (LEPECVD) has been applied to the synthesis of SiGe relaxed buffer layers with Ge end concentrations between 35% and pure Ge. A growth rate of several nanometres per second for relaxed buffer layers is well above that obtainable by any other growth technique. The structural quality of SiGe buffers graded to pure Ge is compared with that of a Ge buffer of constant composition. The structural quality of the pure Ge buffer is remarkably good compared with the much more complicated graded buffer. Complete n-type Si-modulation doped field effect transistor structures have been synthesized by LEPECVD, and the electric properties have been characterized by magneto transport measurements.

Low-temperature heteroepitaxy by LEPECVD

Abstract A new growth technique for low-temperature epitaxy, low-energy plasma-enhanced chemical vapor deposition (LEPECVD) is presented. The plasma enhancement is shown to be very efficient resulting in growth rates in the nm/s range for defect-free epitaxial films at temperatures T≤600°C. We have applied LEPECVD to homoepitaxial growth on Si(001), doped and undoped, and to SiGe heteroepitaxy. The resulting growth rates do not depend on the composition of the reactive gases.

Epitaxial growth at high rates with LEPECVD

Abstract We discuss a new method for plasma enhanced chemical vapor deposition, called low energy plasma enhanced chemical vapor deposition (LEPECVD), applied to the epitaxial growth of Si and SiGe heterostuctures. Growth rates up to 5 nm/s become possible at substrate temperatures below 600°C, by utilizing very intense but low energy plasmas to decompose the reactive gases, SiH 4 and GeH 4 , and by supplying non-thermal energy to enhance the surface kinetics. We have applied LEPECVD to the synthesis of step-graded SiGe buffer layers, and studied them by scanning force microscopy and X-ray reciprocal space mapping.

Phase Transformations in Layered Fe-Si Structures

The kinetics of the phase transformations of the Fe-Si system and the Si/Fe and Fe/Si interfaces have been investigated by 57 Fe conversion electron Mossbauer spectroscopy (CEMS). Single crystalline Fe films grown on Si(111) by molecular beam epitaxy (MBE) and polycrystalline Fe films grown by pulsed laser ablation deposition (PLD) have been thermally treated in vacuum and the formation of the different silicide phases has been monitored as function of temperature and time by CEMS.