Increasing Etch Depth Research Articles

Theoretical Study of Electronic and Thermoelectric Properties of Ultra-Thin Silicene and Germanene

In this study, we used the Non-Equilibrium Green Function (NEGF) and Density Functional Theory (DFT) to analyze the nanoscale electronic properties of silicene and germanene structures, the band structure and Density of State (DOS) for the unit cell of silicene and germanene are found that the energy gap is (0 eV) in both. A comparison was made between silicene and germanene in terms of electrical and thermal properties, by calculating the transmission coefficient T(E) for silicene patterns (Si1, Si2, Si3, and Si4) and germanene patterns (Ge1, Ge2, Ge3, and Ge4). The results show that T(E) decreases with increasing etching depth, which also leads to a decrease in electronic conductivity. Moreover, the value of the Seebeck coefficient (S) increases with increasing drilling depth, and also the sign of S varies from a positive value for (Si1, Si4, Ge1, Ge2, Ge4) to a negative value for (Si2, Si3, Ge3) at Fermi level (Ef) equal to (0 eV). The highest value of the figure of merit is about (1.8) for the Ge4 structure.

Suppression of In-Grown SF Formation and BPD Propagation in 4H-Sic Epitaxial Layer by Sublimating Sub-Surface Damage before the Growth

It is known that basal plane dislocations (BPDs) and in-grown stacking faults (IGSFs) in the 4H-SiC epitaxial layer cause severe electrical degradation in SiC devices. The impact that sub-surface damage (SSD) on a production-grade 4H-SiC substrate with CMP-finished surface causes on both the BPD propagation and IGSF formation during epitaxial growth was investigated by Dynamic AGE-ing (DA). The substrates etched by DA sublimation etching to adjust the residual amount of SSD maintaining a smooth surface without macro step bunching were grown to observe BPD and IGSF density. The obtained results showed that these defect densities decreased exponentially with increasing etching depth. We demonstrated SSD introduced by mechanical processing led BPDs and IGSFs to extend or introduce to the epitaxial layer.

Preparation Process and Quality Characterization of High Density Fine Grain Osmium Target for Coated Cathode

High quality osmium targets are the key influence in improving the emission performance, lifetime and reliability of M-type cathodes. In this experiment, oxidative distillation was used to prepare osmium powder with a purity greater than 99.99%. The effect of hydrogen sintering and hot pressing sintering processes on the densities and grain size of the targets was investigated. The results show that the oxidation distillation process can effectively separate Os from Si, Fe, Ni, Zn and other impurity elements, and the purity of osmium powder prepared by multiple oxidation distillation was not less than 99.99%. Both hydrogen sintering and hot pressing sintering processes can be used to obtain osmium targets with a density of not less than 95%. However, the sintering temperature and time used in the hot pressing sintering process under pressure assistance are significantly lower than those of hydrogen sintering, which is more conducive to inhibiting grain growth during the high densification sintering process. By optimizing the parameters of the hot pressing sintering process, the sintering temperature of 1500°C and the holding time of 1.5h resulted in an osmium target with a density of 99.11% and a grain size of ≤12. XPS analysis of the highly dense fine crystalline osmium targets prepared by hot pressing sintering showed that the C and O mass fractions on the surface of the targets were 0.85% and 4.43% respectively, and the C and O contents gradually decreased with increasing etching depth. The above highly dense and fine crystalline osmium targets can be used in the M-type cathode standard coating process to obtain high purity, dense and strong bonded osmium films.

Optimization design for high-quality factor 1.3 μm InAs/InGaAs quantum dot square microcavity lasers on silicon with output waveguide structures

We, first, demonstrate an optimized structure design and analyze the optical mode properties of 1.3 μm wavelength square microcavity lasers on silicon with InAs/InGaAs quantum-dot active region and mid-point output waveguides. Si-based square microcavities with whispering-gallery-like modes have been proposed for optimizing their quality factors (Q factors). Three-dimensional finite-difference time-domain method is used to numerically analyze the optical mode characteristics. The influences of the side-length of the microcavity, the output waveguide width, and the etching depth on the optical modes of the microcavity are investigated in detail. It indicates that the Q factor increases with increasing etching depth, and decreases rapidly as the waveguide width increases. The results show that with the side length of 18 μm, the waveguide width of 1.0 μm, and the etching depth of 3.5 μm, the Q factor is the highest, and the mode distribution is optimal. The mode wavelength and Q factor are 1305.9 nm and 4694.8, respectively. Advantages of more stable and evenly distributed mode profiles for Si-based square microcavity lasers have been demonstrated, and compared with the Si-based disk microcavity (microdisk) lasers. It promises a potential alternative laser structure for Si-based optoelectronic integration.

Effect of Etching Depth on Threshold Characteristics of GaSb-Based Middle Infrared Photonic-Crystal Surface-Emitting Lasers.

We study the effect of etching depth on the threshold characteristics of GaSb-based middle infrared (Mid-IR) photonic-crystal surface-emitting lasers (PCSELs) with different lattice periods. The below-threshold emission spectra are measured to identify the bandgap as well as band-edge modes. Moreover, the bandgap separation widens with increasing etching depth as a result of enhanced diffraction feedback coupling. However, the coupling is nearly independent of lattice period. The relationship between threshold gain and Bragg detuning is also experimentally determined for PCSELs and is similar to that calculated theoretically for one-dimensional distributed feedback lasers.

Vertical GaN p–n diode with deeply etched mesa and the capability of avalanche breakdown

A simple structure with high breakdown voltage and a low leakage current of a vertical GaN p–n diode on a GaN free-standing substrate is demonstrated. We describe a vertical p–n diode with a simple edge termination that has a drift layer etched deeply and vertically. A device simulation revealed that the electric field was more relaxed at the device edge and applied uniformly in the entire device with increasing etching depth. We fabricated the simulated structure and succeeded in reducing the leakage current and improving the breakdown voltage. With this structure, a stable avalanche breakdown can be observed.

Numerical analysis of the output waveguide design for 1.55 μm square microcavity lasers directly grown on GaAs substrates

We report a structure design of 1.55 μm square microcavity lasers monolithically integrated on GaAs substrates. The mode characteristics of the microcavity lasers are numerically investigated by three-dimensional finite-difference time-domain method. The dependences of the high-quality factor modes on the side length of the microcavity, the width of the output waveguide and the etching depth are investigated in detail. The results demonstrate, for the microcavity structure with the side length of 12 μm, the output waveguide width of 1.0 μm and the etching depth of 3.55 μm, it is optimal to excite high-quality factor modes around wavelength of 1.55 μm. The mode wavelength and the mode quality factor are 1547.46 nm and 2416.28, respectively. The quality factor degrades rapidly with the waveguide width increasing, and increases with increasing etching depth.

Mid-infrared supercontinuum generation in tapered As2S3 chalcogenide planar waveguide

We numerically demonstrate mid-infrared supercontinuum generation in a non-uniformly tapered chalcogenide planar waveguide. This planar rib waveguide of As2S3 glass on MgF2 is 2 cm long with increasing etch depth longitudinally to manage the total dispersion. This waveguide has zero dispersion at two wavelengths. The dispersion profile varies along the propagation distance, leading to continuous modification of the phase-matching condition for dispersive wave emission and enhancement of energy transfer efficiency between solitons and dispersive waves. Numerical simulations are conducted for secant input pulses at a wavelength of 1.55 μm with a width of 50 fs and peak power of 2 kW. Results show this proposed scheme significantly broadens the generated continuum, extending from ~1 to ~7 μm.

Simulation of octave spanning mid-infrared supercontinuum generation in dispersion-varying planar waveguides.

A dispersion-varying tapered planar waveguide is designed to generate supercontinuum efficiently in the mid-infrared region. The rib waveguide of lead-silicate glass on silica is 1.8cm long, consisting of a segment with longitudinally increasing etch depth. The mechanism involves nonlinear soliton dynamics. The dispersion profile is shifted along the propagation distance, leading to continuous modification of the phase-matching condition for dispersive wave (DW) emission and enhancement of energy transfer efficiency between solitons and DWs. With low input pulse energy of 45pJ, simulation demonstrates the generation of both broadband and flat near-octave spectrum spanning 1.3-2.5μm at the -20 dB level.

The GaN-Based Light Emitting Diode Grown on Nanopattern Sapphire Substrate Prepared by Inductively Coupled Plasma Etching

We applied nanoimprint lithography to fabricate nanopattern sapphire substrate. Because the imprint resin cannot endure the inductively coupled plasma bombardment, we use Ni metal to replace the resin as our etching mask. And then, we tuned the parameters to achieve a depth-enough nanopattern sapphire substrate (200-500-nm thick). Then, light emitting diode (LED) structures were grown and the quality was characterized by X-ray diffraction and photoluminescence. The LED tester and integrating sphere were used to analyze the device property. The results could demonstrate that the film quality was improved with increasing etching depth. And, the compressive strain was also released with increasing etching depth. In addition, increasing etching depth could not only improve internal quantum efficiency, but also improve light extraction efficiency. Thus, the external quantum efficiency was enhanced. These evidences demonstrated that nanopatterned sapphire with deeper depth certainly enhanced performance of LEDs.

Influence of subsurface defects on damage performance of fused silica in ultraviolet laser

In ultraviolet pulse laser, damage performance of fused silica optics is directly dependent on the absorptive impurities and scratches in subsurface, which are induced by mechanical polishing. In the research about influence of subsurface defects on damage performance, a series of fused silica surfaces with various impurity concentrations and scratch structures were created by hydrofluoric (HF) acid solution etching. Time of Flight secondary ion mass spectrometry and scanning probe microprobe revealed that with increasing etching depth, impurity concentrations in subsurface layers are decreased, the scratch structures become smoother and the diameter:depth ratio is increased. Damage performance test with 355-nm pulse laser showed that when 600 nm subsurface thickness is removed by HF acid etching, laser-induced damage threshold of fused silica is raised by 40 percent and damage density is decreased by over one order of magnitude. Laser weak absorption was tested to explain the cause of impurity elements impacting damage performance, field enhancement caused by change of scratch structures was calculated by finite difference time domain simulation, and the calculated results are in accord with the damage test results.

HF/HNO3 Etching of the Saw Damage

Wet chemical etching of multicrystalline Si wafer in mixtures of hydrofluoric (HF) and nitric acid (HNO3) combines the removal of the saw damaged silicon lattice on top of the wafer with the creation of a certain surface morphology (texture) on the surface of the underlying bulk silicon. However, it is yet unclear how the kinetics of silicon etching, the constitution of the saw damage, and the resulting surface morphology are related to each other. As a first step to answer this question the etching of the saw damage was studied at three different levels: (i) The development of the surface morphology was studied with increasing etch depth. Regions of key morphological features were identified and parameters describing the morphological development were derived from the surface topography. (ii) The etch rate was studied as parameter that is very sensitive to changes regarding the bonding state of the etched silicon atoms. (iii) The surface chemistry of HF/HNO3 etched Si wafer was monitored by diffuse reflectance Fourier-transform infrared spectroscopy (DRIFT) in order to identify processes that are related to changes in the surface termination of silicon. By the combination of these three approaches a detailed picture from the etching of the saw damage, the development of the texture, and the interaction between structure and etch rate can be drawn.

High-Efficiency Si Solar Cell Fabricated by Ion Implantation and Inline Backside Rounding Process

We introduce a novel, high-throughput processing method to produce high-efficiency solar cells via a backside rounding process and ion implantation. Ion implantation combined with a backside rounding process is investigated. The ion implantation process substituted for thermal POCl3 diffusion performs better uniformity (<3%). The U-4100 spectrophotometer shows that wafers with backside rounding process perform higher reflectivity at long wavelengths. Industrial screen printed (SP) Al-BSF on different etching depth groups was analyzed. SEMs show that increasing etch depth improves back surface field (BSF). The - measurement revealed that etching depths of 6 μm ± 0.1 μm due to having the highest and , it has the best performance. SEMs also show that higher etching depths also produce uniform Al melting and better BSF. This is in agreement with IQE response data at long wavelengths.

Self-organizing nanochannel networks in periodically perforated semiconductor films

In this paper we theoretically analyze the mechanism of nanochannel formation by an evolutionary etching process in periodically perforated semiconductor films. The compressive stresses due to lattice mismatch of the epitaxially grown nanoscale films are gradually relaxed; leading to an evolutionary buckling process. We quantitatively analyze the mechanics of wrinkle evolution around an isolated etch-pit, and a predictive tool to determine the edge-to-corner channel transition is developed. The buckling wavelength increases with increasing etch depth until the etch fronts of neighboring etch-pits merge and multiple channels coalesce. The effect of various system parameters such as etch-pit size, periodicity, and film thickness on the channel morphology has been studied and compared with experimental results. The good agreement provides insight into the physical mechanisms that govern the complex interplay during evolutionary etching and channel formation.

High Efficiency GaN Light-Emitting Diodes With Two Dimensional Photonic Crystal Structures of Deep-Hole Square Lattices

We report the enhanced light extraction of a square lattice photonic crystal GaN LED with a lattice constant of 460 nm and holes with a depth of 500 nm drilled through InGaN/GaN multiple quantum wells (MQWs) using laser holography and inductively coupled plasma reactive ion etching. In spite of the etching through the MQWs leading to undesirable surface recombination, the photonic crystal LEDs exhibited 1.37 times higher light extraction than that of the LEDs without photonic crystals at 20 mA. Theoretical studies using the 3-dimensional finite-difference time domain method show that the increase of the extraction efficiency with increasing etch depth is due to the increase of the density of the leaky modes into the air.

Output power enhancement of light-emitting diodes via two-dimensional hole arrays generated by a monolayer of microspheres

The output power enhancement of the GaN-based light-emitting diodes (LEDs) featuring two-dimensional (2D) hole arrays is demonstrated. The 2D air hole arrays were first generated in the photoresist by utilizing the focusing nature of microspheres, and then transferred onto the GaN surface through dry etching. The maximum output power of the surface-textured LEDs was enhanced by 45% compared with the LEDs without surface texturing. The finite-difference time-domain calculation was performed and revealed that the light extraction efficiency of the textured LEDs increased with increasing etching depth.

InAs 0.45P 0.55/InP strained multiple quantum wells intermixed by inductively coupled plasma etching

The intermixing effect on InAs 0.45P 0.55/InP strained multiple quantum wells (SMQWs) by inductively coupled plasma (ICP) etching and rapid thermal annealing (RTA) is investigated. Experiments show that the process of ICP etching followed RTA induces the blue shift of low temperature photoluminescence (PL) peaks of QWs. With increasing etching depth, the PL intensities are firstly enhanced and then diminished. This phenomenon is attributed to the variation of surface roughness and microstructure transformation inside the QW structure during ICP processing.

Sidewall damage in plasma etching of Si/SiGe heterostructures

Plasma etching is a critical tool in the fabrication of Si/SiGe heterostructure quantum devices, but it also presents challenges, including damage to etched feature sidewalls that affects device performance. Chemical and structural changes in device feature sidewalls associated with plasma-surface interactions are considered damage, as they affect band structure and electrical conduction in the active region of the device. Here the authors report the results of experiments designed to better understand the mechanisms of plasma-induced sidewall damage in modulation-doped Si/SiGe heterostructures containing a two-dimensional electron gas. Damage to straight wires fabricated in the heterostructure using plasma etching was characterized both by measuring the width of the nonconductive “sidewall depletion” region at the device sidewall and by measuring the noise level factor γH/N determined from spectra of the low frequency noise. Observed increases in sidewall depletion width with increasing etch depth are tentatively attributed to the increase in total number of sidewall defects with increased plasma exposure time. Excess negative charge trapped on the feature sidewall could be another contributing factor. Defects at the bottom of etched features appear to contribute minimally. The noise level shows a minimum at an ion bombardment energy of ∼100 eV, while the sidewall depletion width is independent of bias voltage, within experimental uncertainty. A proposed explanation of the noise trend involves two competing effects as ion energy increases: the increase in damage caused by each bombarding ion and the reduction in total number of incident ions due to shorter etch times.

Leakage Current Control in Recessed SiGe Source/Drain Junctions

The impact of different process parameters, namely, the trench etch depth, the total epitaxial thickness, and the epi elevation, on the leakage current of recessed source/drain junctions has been systematically investigated. Besides the behavior of the forward and the reverse currents, attention is also given to the temperature dependence of the leakage current. It is found that both the bulk and the peripheral leakage current density increase strongly with increasing etch depth. Empirically, an exponential dependence has been observed between the area leakage current density at −1 V and the distance between the interface and the electrical p-n junction, whereby an increase by for every of reduction in occurs. This can be understood by the fact that the responsible defects originate mainly at the interface. The perimeter current density shows for certain process splits an exponential dependence on the total thickness of the epitaxial layer , with an increase by a decade for every increase in thickness. Also, the generation and recombination lifetimes have been studied in order to determine an effective energy level of the electrically active defects.

Variation of thin film edge magnetic properties with patterning process conditions in Ni80Fe20 stripes

The authors report the effect of etch depth on the magnetic properties of thin film edges in magnetic nanostructures. In transversely magnetized stripes of 20-nm-thick Ni80Fe20, they use ferromagnetic resonance spectroscopy to measure the edge saturation field and effective out-of-plane stiffness field of the trapped-spin-wave edge mode as a function of ion etch depth. With increasing etching depth, the edge surface angle changes from 47° to 80°, and the field required to saturate the edge magnetization perpendicular to the stripe axis nearly doubles. This trend is largely confirmed by micromagnetic modeling of the edge geometry.