Deepak K. Nayak

High-mobility strained-Si PMOSFET's

Operation and fabrication of a new high channel mobility strained-Si PMOSFET are presented. The growth of high-quality strained Si layer on completely relaxed, step-graded, SiGe buffer layer is demonstrated by gas source MBE. The strained-Si layer is characterized by double crystal X-ray diffraction, photoluminescence, and transmission electron microscopy. The operation of a PMOSFET is shown by device simulation and experiment. The high-mobility strained-Si PMOSFET is fabricated on strained-Si, which is grown epitaxially on a completely relaxed step-graded Si/sub 0.82/Ge/sub 0.18/ buffer layer on Si(100) substrate. At high vertical fields (high |V/sub g/|), the channel mobility of the strained-Si device is found to be 40% and 200% higher at 300 K and 77 K, respectively, compared to those of the bulk Si device. In the case of the strained-Si device, degradation of channel mobility due to Si/SiO/sub 2/ interface scattering is found to be more pronounced compared to that of the bulk Si device. Carrier confinement at the type-II strained-Si/SiGe-buffer interface is clearly demonstrated from device transconductance and C-V measurements at 300 K and 77 K.

Low‐field hole mobility of strained Si on (100) Si1−xGex substrate

Strain Hamiltonian and k⋅p theory are employed to calculate low‐field hole mobility of strained Si layers on (100)Si1−xGex substrate. Nonparabolicity and the warped nature of the valence bands are included. At room temperature, in‐plane hole mobilities of strained Si are found to be 1103 and 2747 cm 2 V−1 s−1 for x equal to 0.1 and 0.2, respectively. These hole mobilities are, respectively, 2.4 and 6 times higher than that of bulk Si. This improvement in the mobility results is mainly due to the large splitting energy between the occupied light‐hole band and the empty heavy‐hole band and smaller effective mass. The effect of p‐type doping on mobility is also presented.

Electrical properties of oxides grown on strained SiGe layer at low temperatures in a microwave oxygen plasma

Microwave plasma oxidation of strained Si1−xGex layer has been carried out at low temperatures (150–200 °C). The chemical properties of the oxide investigated by x‐ray photoelectron spectroscopy show the formation of single phase mixed oxides consisting a SiO2 and GeO2, without any Ge pileup on the surface or at the substrate‐oxide interface. Electrical properties of the oxides show a moderately low value of fixed oxide charge and interface trap density. Grown oxides exhibit low leakage current (10−8 A/cm2) and high breakdown strength (5–10 MV/cm), and are useful for a gate dielectric in metal–oxide semiconductor field effect transistor.

ENHANCEMENT OF RADIATIVE RECOMBINATION IN SI-BASED QUANTUM WELLS WITH NEIGHBORING CONFINEMENT STRUCTURE

Intense photoluminescence (PL) was observed from a new class of Si‐based quantum well structures (QWs), that is, neighboring confinement structure (NCS). NCS consists of a single pair of tensile‐strained‐Si layer and a compressive‐strained Si1−yGey layer sandwiched by completely relaxed Si1−xGex ( layers. In spite of the indirect band structure in real and k spaces, radiative recombination was enhanced compared with not only type‐II strained‐Si/relaxed‐Si1−xGex QWs but also type‐I strained‐Si1−yGey/relaxed‐Si1−xGex QWs. PL without phonon participation was found to dominate the spectrum possibly due to the effective carrier confinement for both electrons and holes. Quantum confinement effect was clearly observed by varying the well width, showing that the expected band alignment is realized.

Band-edge photoluminescence of SiGe/strained-Si/SiGe type-II quantum wells on Si(100)

A high‐quality completely relaxed SiGe buffer layer is grown on Si(100) by gas‐source molecular‐beam epitaxy. A pseudomorphic Si layer is grown on this relaxed SiGe buffer to form SiGe/strained‐Si/SiGe type‐II (staggered) quantum wells. Intense band‐edge photoluminescence is observed from these quantum wells for the first time. The quantum confinement effect in SiGe/strained‐Si/SiGe type‐II quantum wells is demonstrated from the systematic shift of photoluminescence energy peaks with the width of the quantum well. Transitions from the strained‐Si quantum well are identified as radiative recombination of excitons, which are confined into the quantum well.

Properties of SiGe oxides grown in a microwave oxygen plasma

Thin oxide on strained Si1−xGex surface has been grown using a nonelectron cyclotron resonance mode microwave plasma at low temperatures (150–200 °C). An optimized post‐oxidation and post‐metal annealing cycle has resulted in very low fixed oxide charge density (1.78×1010/cm2) and moderately low interface trap density (2.9×1011/cm2 eV). A controlled in situ hydrogen‐plasma treatment to Si1−xGex has been found to be useful in improving the electrical properties of the oxide. The high electron injection phenomena of metal oxide semiconductor capacitors has been used for charge trapping studies of sites normally present in the SiGe oxides. From the position and the extent of current ledge observed as a function of ramped gate voltage, the capture cross section and the total number of traps have been determined.

A comprehensive study of performance and reliability of P, As, and hybrid As/P nLDD junctions for deep-submicron CMOS logic technology

A comprehensive study of P, As, and hybrid As/P nLDD junctions is presented in terms of performance, reliability, and manufacturability for the first time. It is found that As junctions limit the performance of deep submicron devices due to unacceptable hot-carrier reliability, whereas a hybrid junction (light dose P added to medium dose As) dramatically improves hot-carrier reliability while maintaining high performance and manufacturability. For L/sub eff/ of 0.19 /spl mu/m, using this hybrid junction in a manufacturing process, an inverter gate delay of 32 ps, dc hot carrier life time exceeding ten years, and off-state leakage below 30 pA//spl mu/m at 2.9 V have been achieved.

1.54 μm electroluminescence from erbium-doped SiGe light emitting diodes

Er-doped SiGe light emitting diodes were fabricated by implanting Er3+ ions into SiGe epi-layers. The fabricated SiGe:Er diodes show good current–voltage characteristics with a typical reverse breakdown voltage between 10 and 14 V. In the forward bias region, the ideality factor η is found to be 1.84, which indicates that the forward current is dominated by space charge recombinations. By injecting minority carriers into the diodes, Er3+ related emission was observed in the 1.54 μm region at 77 K. To obtain the maximum electroluminescence intensity, the post-implantation annealing under vacuum condition was found to be 800 °C for 30 min.

Hole confinement in a Si/GeSi/Si quantum well on SIMOX

In this work, hole confinement in a MBE-grown Si/GeSi/Si quantum well on SIMOX substrate is investigated in detail using device simulation, electronic measurements, and optical techniques. The hole confinement is clearly demonstrated from GeSi PMOSFET measurements. The experimental results are in good agreement with device simulation results. The quantum confinement of holes in the GeSi quantum well on SIMOX is confirmed using photoluminescence measurements.

Spectral modulation of luminescence of strained Si1−xGex/Si quantum wells in a vertical cavity with air/Si and Si/SiO2 interface mirrors

Integration of strained Si1−xGex/Si quantum wells (QWs) in a vertical cavity is demonstrated on a Si substrate with a buried‐oxide using gas source Si molecular beam epitaxy. Spontaneous emission from the SiGe QW is found to be spectrally coupled to the longitudinal modes of a vertical cavity with buried oxide/Si and top Si/air interface mirrors, which is in excellent agreement with separate reflectance measurements. In addition, clear oscillations were observed in photoluminescence excitation spectra for photon energies even above the Si band gap, demonstrating cavity modulation of the incident light absorption.