Ge Strip Research Articles

Anti-relaxation of tensile lattice strain in Si-embedded Ge strip structure for photonic device applications

This paper reports an anti-relaxation of tensile lattice strain in a narrow Ge strip epitaxially grown on Si by CVD. In an ordinary Ge mesa strip as narrow as 1 μm or below, an in-plane tensile strain as high as 0.2% due to the thermal expansion mismatch with the Si substrate is relaxed by edge-induced relaxation. Such a relaxation is significantly prevented by embedding the Ge strip entirely in Si, as supported by Raman and photoluminescence spectra as well as theoretical strain analysis. This anti-relaxation is effective for efficient optical absorption and light emission at around 1.55 μm.

Infinite lateral growth of (001) single crystal strip in Ge film on SiO2 by micro-chevron laser scanning method

A single crystal strip of Ge, exhibiting a predominant crystal orientation of (001), was successfully grown within a 60 nm thick sputtered Ge film using the micro-chevron laser scanning method. The continuous lateral growth of the Ge strip was achieved through the strategic implementation of a thick cap layer and a SiO2 interlayer between the Ge layer and cap layer. The thick cap layer was pivotal as a heat sink, effectively extending the period during which the Ge film remained molten, preventing unwanted nucleation. Yaw rotation of (001) crystal orientations, which typically trigger the formation of grain boundaries in Si, was found to be negligible in Ge. This observation offers compelling evidence for the potential for infinite lateral growth of (001)-oriented Ge strips. The Raman shift of the single crystal strip was measured at 297.4 cm−1, indicating that the film exhibited tensile stress.

Performance Analysis of Group IV Material Based Tunnel Field Effect Transistor: Effect of Drain Splitting and Introducing Ge-Strip at Source- Channel Junction

The performance effect of splitting and abrupt doping in the drain region, use of a Ge strip at source-channel junction in group IV material based (Ge1 − xSnx/ Si1 − y − zGeySnz) Tunnel Field Effect Transistor (TFET) is investigated in the present manuscript. The variation of certain device parameters, such as mole fraction, different gate dielectrics, gate dielectric thickness and drain doping concentrations are applied to analyze the performance of proposed group IV material based TFET in terms of current-voltage (I-V) characteristics, potential profile and ION/IOFF ratio using device simulator SILVACO TCAD. The simulation results obtained for the proposed TFET structure are compared with the other TFET structures available in the literature, which shows better results as ION/IOFF ratio was received of the order of 1012 in comparison to conventional group IV material based TFET and subthreshold swing of 25.03 mV/decade, which makes the proposed structure promising for high speed switching action with low power CMOS compatibility.

Implementation of lateral Ge–on–Si heterojunction photodetectors via rapid melt growth and self-aligned microbonding for Si photonics

Heterogeneous integration of Ge on a Si lateral p–i–n junction by rapid melt-growth method and self-aligned microbonding is presented. A very thin Ge (100 nm) strip butt-coupled to a Si waveguide for implementing a waveguide photodetector is reported with a low dark current of 1 nA at −3 V bias. The measured 3 dB cut off frequency for the photodetectors is 30 GHz. The internal device responsivity is estimated to be 0.72 A W−1 at the reverse bias of 3 V.

Design and characterization of Ge passive waveguide components on Ge-on-insulator wafer for mid-infrared photonics

We present the design methodology for Ge passive components including single-mode waveguide, grating couplers, multimode interferometer (MMI) couplers, and micro-ring resonators on the Ge-on-insulator wafer at a 1.95 µm wavelength. Characterizations of the fabricated Ge passive devices reveal a good consistence between the experimental and simulation results. By using the Ge micro-ring device, we also reveal that the thermo-optic coefficient in the Ge strip waveguide is 5.74 × 10−4/°C, which is much greater than that in Si.

Formation of large-grain crystalline germanium on single layer graphene on insulator by rapid melting growth

We demonstrate the crystallization of thermally deposited amorphous germanium (Ge) microstrips on single layer graphene (SLG) by rapid melting growth. Lateral growth of large grain crystalline Ge was successfully obtained over entire microstrip structure. SLG has shown its capability to suppress the spontaneous nucleation in the melting Ge, where no or less intermixing of C and Ge atoms has been detected. The interaction of C atoms from the graphene and Ge atoms at the interface is the possible reason for the observation of large compressive strain generated in the Ge strip grown on SLG. This technique provides an innovative breakthrough towards the realization of single-crystalline Ge-on-insulator (GOI) structure on SLG to facilitate the next-generation ultra-large-scale integrated circuits (ULSIs) with multifunctionalities.

Development of a Germanium Small-Animal SPECT System.

Advances in fabrication techniques, electronics, and mechanical cooling systems have given rise to germanium detectors suitable for biomedical imaging. We are developing a small-animal SPECT system that uses a double-sided Ge strip detector. The detector's excellent energy resolution may help to reduce scatter and simplify processing of multi-isotope imaging, while its ability to measure depth of interaction has the potential to mitigate parallax error in pinhole imaging. The detector's energy resolution is <1% FWHM at 140 keV and its spatial resolution is approximately 1.5 mm FWHM. The prototype system described has a single-pinhole collimator with a 1-mm diameter and a 70-degree opening angle with a focal length variable between 4.5 and 9 cm. Phantom images from the gantry-mounted system are presented, including the NEMA NU-2008 phantom and a hot-rod phantom. Additionally, the benefit of energy resolution is demonstrated by imaging a dual-isotope phantom with 99mTc and 123I without cross-talk correction.

Strain Evolution of Ge on Insulator Formed by Rapid Melting Growth

Lateral growth of Ge on insulator was obtained at various annealing temperature by rapid melting growth. The strain distribution of Ge strip was measured with/without SiO2 micro-crucible by micro-Raman. Strain compensating in the Ge stripe between thermal tensile strain and compressive strain were observed. The compressive strain was attributed to the Si-Ge lattice mismatch along the Ge strip. When the Si concentration gradient was lower than ∼3.5%, almost fully-strained Ge strip was obtained. When the Si concentration gradient was larger than ∼3.5%, strain relaxation was observed. The highest average residual compressive strain was about 0.24% in growth region.

Cooling Rate Dependent Lattice Rotation in Ge on Insulators Formed by Rapid Melt Growth

rotated rapidly in the forward section of the Ge strip but slowly in the backward section. The Ge lattice twist monotonically increased with increased soaking temperature. The increase of soaking temperature could induce two factors in the recrystallization process of Ge, which might be related to the twist. First, Si‐Ge interdiffusion was enhanced with increased soaking temperature. The different atomic radii of Si (0.117 nm) and Ge (0.122 nm) may induce strain energy along the strips, which may be related to the lattice rotation in Ge strips. 11 Second, the cooling rate in the recrystallization of Ge decreased with lowered soaking temperature in the RTA process, was determined by the thermal radiation cooling process and requires further investigation. To investigate the relationship between Si‐Ge interdiffusion along the Ge strips and the lattice twist, 150 nm-thick, 2 × 200 μm 2 Ge strips annealed at 967 ◦ C were prepared. Figure 3a shows the typical lattice twist curve of the 200 μm-long Ge strip. The results indicated that a crystal orientation identical to the Si substrate was obtained near the seeding area, and the lattice orientation changed with increased growth length until the end of the strip. Micro-probe Raman spectroscopy measurements were also performed as a function of the distance from the seeding areas. The typical Raman

Room temperature photoluminescence of Ge-on-insulator structures formed by rapid melt growth

Room temperature photoluminescence (PL) was observed along 50 μm long Ge strips on insulator on bulk Si substrates fabricated by rapid melt growth. The PL peaks evidently exhibited a redshift from the origin to the end of the Ge strip because of the shrinkage of the direct bandgap of Ge. Moreover, PL intensities increased along the direction of lateral epitaxial growth primarily because of the decrease in the energy difference between the direct and indirect gaps of Ge. The change in the Ge band structure, which facilitated changes in PL peaks and intensities, was found to have resulted from the variation of tensile strain ratios and Si fractions along Ge strips. Furthermore, the PL intensity at the end of the strip was one magnitude higher than that of bulk Ge, which indicates the high quality of Ge-on-insulator structures.

Cocaine detection by a mid-infrared waveguide integrated with a microfluidic chip

A germanium (Ge) strip waveguide on a silicon (Si) substrate is integrated with a microfluidic chip to detect cocaine in tetrachloroethylene (PCE) solutions. In the evanescent field of the waveguide, cocaine absorbs the light near 5.8 μm, which is emitted from a quantum cascade laser. This device is ideal for (bio-)chemical sensing applications.

Recent developments in semiconductor gamma-ray detectors

The successful development of lithium-drifted Ge detectors in the 1960s marked the beginning of the significant use of semiconductor crystals for direct detection and spectroscopy of gamma-rays. In the 1970s, high-purity Ge became available, which enabled the production of complex detectors and multi-detector systems. In the following decades, the technology of semiconductor gamma-ray detectors continued to advance, with significant developments not only in Ge detectors but also in Si detectors and room-temperature compound-semiconductor detectors. In recent years, our group at Lawrence Berkeley National Laboratory has developed a variety of gamma-ray detectors based on these semiconductor materials. Examples include Ge strip detectors, lithium-drifted Si strip detectors, and coplanar-grid CdZnTe detectors. These advances provide new capabilities in the measurement of gamma-rays, such as the ability to perform imaging and the realization of highly compact spectroscopy systems.

Development of a Gamma-Ray Box (GARBO)

Isomer decays, β–γ and electron–γ spectroscopy, α–γ fine structure studies, and Coulomb excitation are cases of nuclear structure experiments where the ideal detector is a compact, highly segmented, very efficient germanium (Ge) detector box. In order to develop such a structure, we are working on the R&D of large, segmented, high-purity planar Ge strip detectors (HPGeDSSD) which form the walls of such a box. We have developed a 92mm×92mm×20mm HPGeDSSD, which has 16×16 orthogonal strips of 5mm width. We are in the process of designing a focal plane detector for the Argonne fragment mass analyzer which consists of a five-sided box, each side having a HPGeDSSD backed by a large segmented clover HPGe detector. MCNP simulations indicate this detector would have an efficiency of ∼60% for 122keV gamma rays and ∼15% for 1.33MeV radiation, which is ideal for studying the decays of nuclei far from stability that are usually produced with very low cross-sections.