Intrinsic Si Substrates Research Articles

Experimental Study of Near-field Radiative Heat Transfer Between Large-Area Polar Dielectric Films

Utilizing polar dielectric films can improve the performance of near-field thermophotovoltaic system. To confirm the enhancement of near-field radiative heat transfer (NFRHT) achieved by large-area polar dielectric films, we built an experimental setup and observe NFRHT between two 250 nm-thick SiO2 films on intrinsic Si substrate with an area 5 × 5 mm2. The two films are supported by SiO2 nano-spacers with a height of 302 nm. Temperature difference between the two films varies from 13 K to 42 K at room temperature. The observed near-field radiative heat flux closely matches the theoretical values, which surpasses substrate-only system by up to 9.87 times and could reach up to 7.45 times that of blackbody radiation due to excitation of the surface photon polaritons modes. These results demonstrate the effectiveness of polar dielectric films in enhancing NFRHT.

Ge0.92Sn0.08/Ge multi-quantum-well LEDs operated at 2-μm-wavelength on a 12-inch Si substrate

The development of an efficient group-IV light source that is compatible with the CMOS process remains a significant goal in Si-based photonics. Recently, the GeSn alloy has been identified as a promising candidate for realizing Si-based light sources. However, previous research suffered from a small wafer size, limiting the throughput and yield. To overcome this challenge, we report the successful growth of GeSn/Ge multiple-quantum-well (MQW) p-i-n LEDs on a 12-inch (300-mm) Si substrate. To the best of our knowledge, this represents the first report of semiconductor LEDs grown on such a large substrate. The MQW LED epitaxial layer is deposited on a 12-inch (300-mm) (001)-oriented intrinsic Si substrate using commercial reduced pressure chemical vapor deposition. To mitigate the detrimental effects of threading dislocation densities on luminescence, the GeSn/Ge is grown pseudomorphically. Owing to the high crystal quality and more directness in the bandgap, enhanced electroluminescence (EL) integrated intensity of 27.58 times is demonstrated compared to the Ge LED. The MQW LEDs exhibit EL emission near 2 μm over a wide operating temperature range of 300 to 450 K, indicating high-temperature stability. This work shows that GeSn/Ge MQW emitters are potential group-IV light sources for large-scale manufacturing.

The Anti-Reflection Coating Design for the Very-Long-Wave Infrared Si-Based Blocked Impurity Band Detectors

An anti-reflection coating on a back-illuminated 128 × 128 array Si-based blocked impurity band (BIB) detector in a very-long-wave infrared range was designed in this work. The reflectance and transmittance spectra of ZnS films with different thicknesses on intrinsic Si substrates were studied with a FDTD simulation and experiment. Compared to bare Si substrate, the reflectance of Si coated with 1.5, 2.0, 2.5, and 3.0 μm thick ZnS significantly decreased, while the transmittance increased in the range of 10.0~25.0 μm band. The transmittance enhancement ratio reached approximately 32%, 32%, 28%, and 29%, respectively. It was evidenced that the enhanced transmission at a specific wavelength was caused by the effective interference cancellation effect. Then, a 2.0 μm thick ZnS thin film was deposited on the backside of the 128 × 128 array Si-based BIB detector. The spectral responsivity of the detector increased significantly. Additionally, the blackbody responsivity increased by approximately 36%, suggesting that the ZnS film is an ideal anti-reflection material for VLWIR detectors in the range of 10.0~25.0 μm band.

Wavelength Modulation Characteristics of Metal Gratings on Si-Based Blocked-Impurity-Band (BIB) Terahertz Detectors.

In this work, the wavelength selection characteristics of metal gratings on Si-based blocked-impurity-band (BIB) detectors in the terahertz band were studied by performing experiments and a finite difference time domain (FDTD) simulation. The transmission spectra of metal gratings with different periods on 130 μm intrinsic Si substrates were measured. When the metal grating period increased from 16 to 20 to 32 μm, the peak position of the spectrum moved from 21.71 to 24.50 to 36.59 μm, which is in good agreement with the FDTD simulation results. The structure with the period of 32 μm shows the best wavelength selective transmission characteristics. Then, the bare Si-based BIB devices and metal grating/Si-based BIB hybrid devices with different thicknesses of blocking layers of 2 and 5 μm were fabricated. By covering different periods of metal gratings for the devices with a thicker blocking layer of 2 μm, we obtained more effective wavelength selection characteristics and stronger response spectra enhancement ratios that were about 1.3, 2.4, or 1.9 times. This was mainly due to the localized optical field enhancement effect of the plasmons resonance in metal gratings, which decays exponentially in a vertical direction. Our results demonstrate a new approach for the Si-based BIB detector to realize multiband selective detection applications.

Interface electric field confinement effect of high-sensitivity lateral Ge/Si avalanche photodiodes

A novel lateral Ge/Si avalanche photodiode without a charge region is investigated herein using device physical simulation. High field is provided by the band-gap barrier and build-in field at the Ge/Si interface in the vertical direction. Modulating the Si mesa thickness (0-0.4 μm) and impurity concentration of the intrinsic Si substrate (1 × 10 16 -4 × 1016 cm -3 ) strengthens the electric field confinement in the substrate region and provides a high avalanche multiplication in the Si region. When the Si mesa thickness is 0.3 μm, and the impurity concentration of the Si substrate is 2 × 10 16 cm -3 , the Lateral Avalanche PhotoDiode (LAPD) exhibits a peak gain of 246 under 1.55 μm incident light power of -22.2dBm, which increases with decreasing light intensity.

Epitaxial growth of germanium thin films on crystal silicon substrates by solid phase crystallization

We have investigated the solid phase crystallization (SPC) of amorphous germanium (a-Ge) precursors on single crystalline silicon (c-Si) substrates as seed layers and successfully obtained the epitaxial growth of Ge. The n-type (100) Si substrate is most suitable for preferential growth following the substrate orientation, because the velocity of preferential growth is higher than those on the other substrates and preferential growth is completed before random nucleation. The impurity contamination in the a-Ge precursors probably enhances random nucleation. The epitaxial growth is disturbed by the impurity contamination at a relatively high SPC temperature in the intrinsic and p-type Si substrates with the (100) orientation and the n-type and intrinsic Si substrates with the (111) orientation, because the lower velocity of preferential growth allows random crystallization. Almost no epitaxial growth is observed on the p-type (111) Si substrates even when low-impurity a-Ge precursors are used.

High-Contrast Imaging of Graphene via Time-Domain Terahertz Spectroscopy

We demonstrate terahertz (THz) imaging and spectroscopy of single-layer graphene deposited on an intrinsic Si substrate using THz time-domain spectroscopy. A single-cycle THz pulse undergoes multiple internal reflections within the Si substrate, and the THz absorption by the graphene layer accumulates through the multiple interactions with the graphene/Si interface. We exploit the large absorption of the multiply reflected THz pulses to acquire high-contrast THz images of graphene. We obtain local sheet conductivity of the graphene layer analyzing the transmission data with thin-film Fresnel formula based on the Drude model.

Reduced microwave loss in trenched superconducting coplanar waveguides

Reducing the contribution of all sources of microwave loss is important for increasing coherence times in superconducting qubits. In this paper we investigate reducing the loss by systematically removing Si substrate material from the gap region in titanium nitride coplanar waveguides fabricated on intrinsic Si substrates. By exploiting the radial dependence of the etch rate in a parallel plate reactive ion etcher, otherwise identical coplanar waveguides with only the Si gaps etched to varying depth, i.e., trenched, were created in a single TiN film within a single processing step. Measurements at these multiple depths permit the study of the loss reduction in isolation to the unintentional effects caused by any single processing step. When comparing the loss from all trench depths we found that the high power loss was similar, but in the single photon limit the loss was reduced by a factor of two for deeper trenches in agreement with predictions from finite element analysis.

Effects of annealing temperature on the characteristics of silicate/HfO2 insulator formed on the p-Si/Si0.8Ge0.2 and p-Si/Si0.8Ge0.2/intrinsic-Si (20Å) substrates

We successfully deposited the reliable silicate/HfO2 insulator films on both p-Si/Si0.8Ge0.2 and p-Si/Si0.8Ge0.2/intrinsic-Si substrates via the oxidation and annealing of thin Hf film deposited by rf-magnetron sputtering. The oxidation of Hf metal films results in the electrically stable silicate/HfO2 stacked layers. The silicate films (i.e., a layer of Hf–Si–Ge–O) were formed between the HfO2 film and the p-Si/Si0.8Ge0.2 substrate. We found that the Ge segregation is suppressed by the insertion of a 2-nm-thick Si-overlayer on the Si0.8Ge0.2 substrate, resulting in better electrical properties than those obtained from the samples without the Si-overlayer. High-temperature annealing at 700 °C causes the diffusion of Ge into the silicate/HfO2 stacked insulator films only for the samples without the Si-overlayer. In addition, 700 °C annealing results in the formation of a thin SiOx layer at the silicate–Si0.8Ge0.2 substrate regardless of the presence of the Si-overlayer.

The combined effects of strain and heavy doping on the indirect band gap of Si and Ge xSi 1− x alloys

Both boron and phosphorus cause shrinkage in the lattice constant of Si. Therefore heavily doped Si:B and Si:P epitaxial layers grown on intrinsic Si substrates are strained provided no misfit dislocations are present at the interface. The strain is a biaxial extension and has a hydrostatic component as well as a shear component. Ge x Si 1− x layers matched to Si or Ge substrates are also strained. The strain causes band splitting which in its turn causes narrowing of the fundamental indirect band gap of the layers. The hydrostatic component also causes band gap shrinkage. In addition the strain modifies and increases the band gap narrowing due to heavy doping effects as compared with the unstrained case. In this paper the narrowing of the fundamental indirect band gap due to the combined effects of strain and heavy doping is calculated for Si and Ge x Si 1− x epilayers. The results are used to explain the photoluminescence of heavily doped Si:B strained layers grown by MBE on intrinsic Si substrate. It is shown that the band gap narrowing due to heavy doping in strained Ge x Si 1− x layers must be taken into account in the design of double heterostructure bipolar transistors with Ge x Si 1− x base layers.