Properties Of Epitaxial Layers Research Articles

Effects of low fluence 212 MeV Ge swift heavy ion irradiation on the structural and optical properties of β-Ga2O3 epitaxial layers

Considering the future applications of the ultra-wide bandgap semiconductor β-Ga2O3 in high-performance electronic devices and aerospace, the effects of low fluence 212 MeV Ge swift heavy ion (SHI) irradiation on the structural and optical properties of β-Ga2O3 epitaxial layers have been studied in this work. The alternations in Raman scattering properties of the epitaxial layer after Ge SHI irradiation indicate the generation of lattice defects. The increased concentration of oxygen vacancies after irradiation leading to an enhanced area ratio of the yellow-red emission band in the PL spectrum of the β-Ga2O3 epitaxial layer. Simultaneously, the PL intensity quenches as the irradiation fluence increases, attributed to the generation of non-radiative recombination centers. Furthermore, HRTEM analysis provides direct evidence of lattice damage caused by 212 MeV Ge SHI irradiation to the samples. The results demonstrate that the spectral behaviors of β-Ga2O3 epitaxial layers can be modulated by low fluence Ge SHI irradiation with less damage caused to the overall crystalline quality and structure.

Driving up the quality of metal organic chemical vapor deposition-grown epitaxial wafers for highly innovative photonic applications

Quantum cascade lasers (QCL) and extended InGaAs photodetectors (ex-PDs) (operating in regime 1.9–2.6 µm wavelength) are very attractive materials for use in sophisticated photonics and microelectronics such as optical recording, scanners, laser spectroscopy, thermal or gas sensing. Once a laboratory curiosity, QCLs and ex-PDs are now becoming commercially available products, shaping exciting applications. In this work, we present the intricacies and challenges of the development and industrial production of Metal Organic Chemical Vapor Deposition (MOCVD)-grown QCL and ex-PD structures as well as demonstrate their viability for large-scale manufacturing.Different types of epitaxial structures were grown using a multi-wafer production MOCVD system, in 12 × 3″ wafer configuration per growth run. Structural and electrical properties of epitaxial layers were carefully examined.MOCVD growing of QCL and ex-PD structures is a very demanding process. MOCVD production reactor enables development of highly complicated chemical reactions, however, as gas residence is much longer than in small R&D systems, the hetero-interfaces of InGaAs/InAlAs are inevitably graded, which negatively impacts optical and electrical parameters of QCL devices. In addition, QCL structure requires the exact layer thickness as well as absolute precision and repeatability when developing strained InAlAs and InGaAs epi‑layers. In the case of ex-PDs fabrication, the crucial thing is to develop a specially designed and graded buffer layer, and to avoid numerous misfit defects and anomalies in dark current. We obtained high crystallographic quality and repeatability of the epi‑layers, which resulted in QCL high-performance continuous-wave operation and fabrication of ex-PDs with low dark current density (less than 1 × 10−4 A/cm2 at -100 mV/room temperature (RT)) achieving results consistent with Rule07 and higher quantum efficiency.

On Model for Prognosis of Mass Transport During Magnetron Sputtering

In this paper we analyze mass transfer during growth of epitaxial layers in magnetrons. Due to analysis of influence of physical and technological parameters on the growth we formulate several recommendations to improve properties of epitaxial layers: increase of homogeneity of films; minimization of defects of films; dependence of properties of heterostucture on geometric dimensions of magnetron (in fact this is correlation between the above geometric dimensions and growth time). We introduce an analytical approach for analyzing mass transfer. The approach gives a possibility to take into account the nonlinearity of processes, as well as changes in parameters in space and time.

Laser-assisted local metal-organic vapor phase epitaxy.

Selective area epitaxial growth is an important technique, both for monolithic device integration as well as for defect reduction in heteroepitaxy of crystalline materials on foreign substrates. While surface engineering with masking materials or by surface structuring is an effective means for controlling the location of material growth, as well as for improving crystalline properties of epitaxial layers, the commonly involved integral substrate heating presents a limitation, e.g., due to constraints ofr the thermal budget applicable to existing device structures. As a solution, an epitaxial growth approach using a laser source only locally heating the selected growth area, in combination with metal-organic precursors to feed a pyrolithic chemical reaction (also known as metal-organic vapor phase epitaxy, MOVPE), is presented. Without masking or surface structuring, local epitaxial growth of III-V compound semiconductor layers on a 50-1500 µm length-scale, with high structural and optical quality, is demonstrated. We discuss general design rules for reactor chamber, laser heating, temperature measurement, sample manipulation, gas mixing, and distinguish laser-assisted local MOVPE from conventional planar growth for the important compound semiconductor GaAs. Surface de-oxidation prior to growth is mandatory to realize smooth island surfaces. Linear growth rates in the range 0.5-9 µm/h are demonstrated. With increasing island diameter, the probability for plastic deformation within the island increases, depending on reactor pressure. A step-flow mode on the island surface can be achieved by establishing a sufficiently small temperature gradient across the island.

Epitaxial Growth and Characterization of 4H-SiC for Neutron Detection Applications

The purpose of this work is to study the 4H-SiC epitaxial layer properties for the fabrication of a device for neutron detection as an alternative material to diamond detectors used in this field. We have studied a high growth rate process to grow a thick epitaxial layer (250 µm) of 4H-SiC and, in order to estimate the quality of the epitaxial layer, an optical characterization was done through Photoluminescence (PL) spectroscopy for stacking fault defect evaluation. Micro Raman spectroscopy was used for simultaneous determination of both carrier lifetime and induced carriers in equilibrium. We have compared these results with other two samples with an epitaxial layer of 100 micron, obtained with two different growth rates, 60 and 90 µm/h, respectively. From Raman measurements it has been observed that both the growth rate and the grown epitaxial layer thickness have an effect on the measured carrier lifetime. A comparison between different kinds of stacking faults (SF) was done, evaluating the influence of these defects on the carrier lifetime as a function of the injection level and it was observed that only at a low injection is the effect on the carrier lifetime low.

Structural Quality and Magnetotransport Properties of Epitaxial Layers of the (Ga,Mn)(Bi,As) Dilute Magnetic Semiconductor.

Structural analysis of epitaxial layers of the (Ga,Mn)(Bi,As) quaternary dilute magnetic semiconductor (DMS), together with investigations of their magnetotransport properties, has been thoroughly performed. The obtained results are compared with those for the reference (Ga,Mn)As layers, grown under similar conditions, with the aim to reveal an impact of Bi incorporation on the properties of this DMS material. Incorporation of Bi into GaAs strongly enhances the spin-orbit coupling strength in this semiconductor, and the same has been expected for the (Ga,Mn)(Bi,As) alloy. In turn, importantly for specific spintronic applications, strong spin-orbit coupling in ferromagnetic systems opens a possibility of directly controlling the direction of magnetization by the electric current. Our investigations, performed with high-resolution X-ray diffractometry and transmission electron microscopy, demonstrate that the (Ga,Mn)(Bi,As) layers of high structural quality and smooth interfaces can be grown by means of the low-temperature molecular-beam epitaxy method, despite a large difference between the sizes of Bi and As atoms. Depending on the applied buffer layer, the DMS layers can be grown under either compressive or tensile misfit strain, which influences their magnetic properties. It is shown that even small 1% Bi content in the layers strongly affects their magnetoelectric properties, such as the coercive field and anisotropic magnetoresistance.

On increasing the homogeneity of the properties of epitaxial layers grown from the gas phase, taking into account natural convection and changes in the rate of chemical interaction between materials

In this paper, using the recently introduced analytical approach for the analysis of mass and heat transfer during film growth in reactors for epitaxy from the gas phase, these processes are analyzed taking into account natural convection and the possibility of changing the rate of chemical interaction between reagents. As a result of the analysis, the conditions under which the homogeneity of the grown epitaxial layers increases with a change in the values of the parameters of the growth process are formulated.

On prognosis of variation of properties of epitaxial layers by choosing of temperature field during growth

On prognosis of variation of properties of epitaxial layers by choosing of temperature field during growth

Raman spectra of GaSe epitaxial layers grown on GaAs substrates and group-theoretical analysis of their vibrational modes

A complete group-theoretical analysis of vibrational modes in ε, β, γ-GaSe polytypes has been performed. Raman spectroscopy data obtained on single crystals of ε-GaSe with a subsequent group-theoretical analysis were used to analyze the Raman spectra low-dimensional GaSe structures. Information was obtained on the structural properties of epitaxial layers and arrays of nanorods of the ε-polytype GaSe grown by molecular beam epitaxy on GaAs (001) substrates.

On improvement of films growth from gas with natural convection and chemical interaction

In this paper, the authors introduce an analytical approach for the analysis of mass and heat transfer during the growth of film in reactors for gas-phase epitaxy. The epitaxial processes were analyzed with natural convection and possibility of changing the rate of chemical interaction between reagents. As a result of the analysis, the authors obtained conditions on physical and technological parameters for increasing the homogeneity of the grown epitaxial layers. The authors compare growth regimes at normal and low pressure of reagents and gas-carrier. The authors also analyzed dependences of properties of epitaxial layers on the frequency of rotation of substrate holder, on the diffusion coefficients of reagents, on the kinematic viscosity and on the input velocity. The authors compared their results of calculation with recently obtained experimental data and obtained enough good agreement. All analytical results without experimental verification have been checked by numerical simulation with using independent approaches.

Changing of properties of epitaxial layers by choosing of temperature field during growth

Changing of properties of epitaxial layers by choosing of temperature field during growth

Robustness of ferromagnetism in (In,Fe)Sb diluted magnetic semiconductor to variation of charge carrier concentration

The influence of He+ ion irradiation on the transport and magnetic properties of epitaxial layers of a diluted magnetic semiconductor (DMS) (In,Fe)Sb, a two-phase (In,Fe)Sb composite and a nominally undoped InSb semiconductor has been investigated. In all layers, a conductivity type conversion from the initial n-type to the ptype has been found. The ion fluence at which the conversion occurs depends on the Fe concentration in the InSb matrix. Magnetotransport properties of the two-phase (In,Fe)Sb layer are strongly affected by ferromagnetic Fe inclusions. An influence of the number of electrically active radiation defects on the magnetic properties of the single-phase In0.75Fe0.25Sb DMS has been found. At the same time, the results show that the magnetic properties of the In0.75Fe0.25Sb DMS are quite resistant to significant changes of the charge carrier concentration and the Fermi level position. The results confirm a weak interrelation between the ferromagnetism and the charge carrier concentration in (In,Fe)Sb.

Analysis of Possibility of Growth of Several Epitaxial Layers Simultaneously In Gas Phases Framework One Technological Process. On Possibility to Change Properties of Epitaxial Layers

Analysis of Possibility of Growth of Several Epitaxial Layers Simultaneously In Gas Phases Framework One Technological Process. On Possibility to Change Properties of Epitaxial Layers

Analysis of Possibility of Growth of Several Epitaxial Layers Simultaneously in Gas Phases Framework One Technological Process. On Possibility to Change Properties of Epitaxial Layers

Analysis of Possibility of Growth of Several Epitaxial Layers Simultaneously in Gas Phases Framework One Technological Process. On Possibility to Change Properties of Epitaxial Layers

Effect of germanium doping on electrical properties of n-type 4H-SiC homoepitaxial layers grown by chemical vapor deposition

The effect of germanium (Ge) on n-type 4H-SiC is experimentally studied by electrical characterization of homoepitaxial layers grown by chemical vapor deposition (CVD). Measurements show that electrical properties of epitaxial layers can be changed by intentional incorporation of germane (GeH4) gas during the deposition process. On the nanoscale, two-dimensional mappings acquired with conductive atomic force microscopy show preferential conductive paths on the surface of Ge-doped samples, which are related to the presence of this isoelectronic impurity. Hall effect measurements confirm that also macroscopic electrical properties of n-type 4H-SiC are improved due to incorporation of Ge into SiC during CVD growth. In particular, despite equal free electron concentration, enhanced mobility in a wide temperature range is measured in Ge-doped samples as compared to a pure 4H-SiC layer. Based on our results from Hall effect measurements as well as admittance spectroscopy and deep level transient spectroscopy, it is speculated that Ge influences the generation and annealing of other point defects and thus helps to reduce the total concentration of defects.

On optimization of growth from gas phase in a vertical reactor with account native convection to improve properties of films

Purpose The purpose of this paper is to: analyze the changing properties of epitaxial layers, manufactured in the considered reactor, with the changing parameters of the growth taking into account native convection; and development of the most common analytical approach to describe the technological process. Design/methodology/approach In this paper a vertical reactor for gas phase epitaxy is considered that consists of an external casing, a keeper of substrate with a substrate and a spiral around the casing in area of the growth zone to generate induction heating in order to activate the chemical reactions in the decay of reagents and the growth of the epitaxial layer by using the reagents. The authors introduce an analytical approach to analyze nonlinear mass and heat transport with account variation in space and time parameters. Findings The authors find conditions to improve properties of epitaxial layers. Originality/value Growth regimes at atmospheric and low pressure have been compared and analyzed for their influence of the native convection on the growth of the epitaxial layers. Accounting for the calculated results, recommendations have been formulated to improve the properties of the epitaxial layers.

Advances in 3x150 mm Hot-Wall and 6x150 mm Warm-Wall SiC Epitaxy for 10kV-Class Power Devices

Initial results from a custom, 3x150 mm horizontal hot-wall, SiC Vapor-Phase epitaxial growth reactor (VPE), with full planetary motion are reported. Epitaxial layer properties are compared with those grown on previously reported 1x150 mm hot-wall and 6x150 mm warm-wall reactors for epitaxial wafers of up to 100 microns thickness. The median intra-wafer thickness and doping uniformity (σ/mean) for the 3x150 mm reactor are 0.9% and 6.10%, respectively. The intra-run thickness and doping variation are 0.18% and 1.01%. The projected 5x5 mm useable area for layers of nominal 5 to 30 μm thickness for all the reactor configurations (as measured by a Candela CS2 optical surface analyzer) are approximately 92%, corresponding to an effective defect density of about 0.35 cm-2. Useable areas as high as 86.5% and 1-2 nm rms roughness have been observed for layers of over 100 μm thickness. Initial morphological results using a higher resolution, LaserTec SICA6X confocal differential interference contrast (CDIC) microscope, are also presented.

Charge collection and non-ionizing radiation tolerance of CMOS pixel sensors using a 0.18 μm CMOS process

The proposed Circular Electron Positron Collider (CEPC) will be primarily aimed for precision measurements of the discovered Higgs boson. Its innermost vertex detector, which will play a critical role in heavy-flavor tagging, must be constructed with fine-pitched silicon pixel sensors with low power consumption and fast readout. CMOS pixel sensor (CPS), as one of the most promising candidate technologies, has already demonstrated its excellent performance in several high energy physics experiments. Therefore it has been considered for R&D for the CEPC vertex detector. In this paper, we present the preliminary studies to improve the collected signal charge over the equivalent input capacitance ratio (Q/C), which will be crucial to reduce the analog power consumption. We have performed detailed 3D device simulation and evaluated potential impacts from diode geometry, epitaxial layer properties and non-ionizing radiation damage. We have proposed a new approach to improve the treatment of the boundary conditions in simulation. Along with the TCAD simulation, we have designed the exploratory prototype utilizing the TowerJazz 0.18μm CMOS imaging sensor process and we will verify the simulation results with future measurements.

Pb1–x Eu x Te alloys (0 ⩽ x ⩽ 1) as materials for vertical-cavity surface-emitting lasers in the mid-infrared spectral range of 4–5 μm

The optical properties of epitaxial layers and heterostructures based on Pb1–xEuxTe alloys (0 ⩽ x ⩽ 1) are analyzed in the context of designing Bragg mirrors and vertical-cavity surface-emitting lasers for the midinfrared spectral range. It is shown that the optimal heteropair for laser microcavities is Pb1–xEuxTe(x ≈ 0.06)/EuTe. On the basis of this heteropair, highly reflective Bragg mirrors consisting of just three periods and featuring a reflectance of R ⩾ 99.8% at the center of the stop band are grown by molecular-beam epitaxy on BaF2 (111) substrates. Single-mode optically pumped vertical-cavity surface-emitting lasers for the 4–5 μm spectral range operating at liquid-nitrogen temperatures are demonstrated.

On Prognosis of Epitaxy from Gas Phase Process to Improve Properties of Epitaxial Layers

In this paper we analyzed mass and heat transport in a reactor from gas phase during growth an epitaxial layer. Based on results of the analysis we analyzed dependences of properties of grown layers on parameters of technological process.