Net Carrier Concentration Research Articles

Development and morphological analysis of the zone refining process for high purity germanium

A highly efficient purification process has been developed to enhance the purity of germanium (Ge) up to 13 N from an initial 4N purity. Hall effect measurements demonstrated that part of the zone refined Ge (ZRGe) bars exhibited p-type conductivity and high purity with a net charge carrier concentration of around 4–9 × 1010 cm−3. Noteworthy observations include a rise in carrier concentration (1011 to 1012 cm−3) at a very low zone refining (ZR) velocity of 1 mm/min, which is attributed to the diffusion of impurities from the container into the Ge melt. The purification efficiency was enhanced by optimizing the ZR velocity to around 4–5 mm/min. Purification was carried out at different process steps using graphite and quartz containers. Subsequent microstructural examinations, conducted in conjunction with wet-chemical etching of the sample unveiled the presence of various grains, grain boundaries (GBs), and low & high-density of dislocation clusters: These observations were made in samples that had undergone zone refining under various gas atmospheres including argon, nitrogen and hydrogen. Electron back scattered diffraction (EBSD) analysis reveals the characteristics of multiple grains and grain boundaries (GBs) of Ge refined in argon and nitrogen atmosphere, including low-angle GBs, high-angle GBs with coincide site lattice (CSL) Σ3, Σ9, Σ27a, and random angle GBs. In contrast, the EBSD results of Ge refined in hydrogen atmosphere shows larger grains with only a few low-angle grain boundaries. The materials refined in argon and nitrogen show a lower carrier lifetime (10–30 μs) owing to the presence of various high angle grains boundaries as well as low purity. Conversely, zone refining in hydrogen resulted in the carrier lifetime of around 50 μs in polycrystalline Ge wafers with larger grains.

Metal‐Organic Chemical Vapor Deposition Regrowth of Highly Doped n+ (In)GaN Source/Drain Layers for Radio Frequency Transistors

Herein, epitaxially regrown n+ (In)GaN source/drain layers for radio frequency high electron mobility transistors, addressing material and electrical characterization, are reported. A range of n+ GaN and n+ InGaN layers with indium 4–12 at% and silicon 0–5.1 × 1020 cm−3 are evaluated. The active carrier concentration in n+ InGaN exceeds 2 × 1020 cm−3. The layers exhibit so‐called V‐defects, observed by atomic force microscope and transmission electron microscope (TEM), which are associated with local composition changes. In addition to the high Si doping levels, nitrogen vacancies are also considered to contribute toward their net carrier concentration. Due to its relevance for device processing, selectivity analysis is performed, and the optimal process conditions for selective regrowth are identified. Regrowth under high temperature (800 °C) is found to be conducive to improved selectivity. However, a high thermal budget negatively impacts the overall regrowth process, as reported here for In0.17Al0.83N and Al0.26Ga0.74N barriers: whereas the InAlN barrier suffers from intermixing, the AlGaN barrier demonstrates high‐temperature stability. The impact of intermixing is studied from complementary TEM and DC electrical measurements. A low overall contact resistance of 75 Ω μm is obtained with the regrown n+ InGaN layers.

Current transport mechanism of lateral Schottky barrier diodes on β-Ga2O3/SiC structure with atomic level interface

Heterogeneous integration of β-Ga2O3 on highly thermal conductive SiC substrate by the ion-cutting technique is an effective solution to break the heat-dissipation bottleneck of β-Ga2O3 power electronics. In order to acquire high-quality β-Ga2O3 materials on SiC substrates, it is essential to understand the influence of the ion-cutting process on the current transport in β-Ga2O3 devices and to further optimize the electrical characteristics of the exfoliated β-Ga2O3 materials. In this work, the high quality of β-Ga2O3/SiC structure was constructed by the ion-cutting process, in which an amorphous layer of only 1.2 nm was formed between β-Ga2O3 and SiC. The current transport characteristics of Au/Pt/Ni/β-Ga2O3 Schottky barrier diodes (SBDs) on SiC were systematically investigated. β-Ga2O3 SBDs with a high rectification ratio of 108 were realized on a heterogeneous β-Ga2O3 on-SiC (GaOSiC) substrate. The net carrier concentration of the β-Ga2O3 thin film for GaOSiC substrate was down to about 8% leading to a significantly higher resistivity, compared to the β-Ga2O3 donor wafer, which is attributed to the increase in acceptor-type implantation defects during the ion-cutting process. Furthermore, temperature-dependent current–voltage characteristics suggested that the reverse leakage current was limited by the thermionic emission at a low electric field, while at a high electric field, it was dominated by the Poole–Frenkel emission from E3 deep donors caused by the implantation-induced GaO antisite defects. These results would advance the development of β-Ga2O3 power devices on high thermal conductivity substrate fabricated by ion-cutting technique.

Properties of a highly compensated high-purity germanium

The electrical and optical properties of a compensated high-purity germanium (HPGe) single crystal was investigated using various characterization techniques. Aluminium, boron, and phosphorus were the major residual shallow-level impurities identified by photothermal ionization spectroscopy (PTIS). Hall effect measurements performed at low temperatures (77 K) along the growth length reveal that the crystal is p-type at the top and bottom, while n-type in the middle part with a net carrier concentration in the range of 1010–1011 cm−3. The obtained very high resistivity (2.3 ⨯ 108 Ω·cm) at 91 K in the temperature-dependent Hall measurements (TDH) at the bottom part of the crystal indicates a high level of compensation (84%) of charge carriers by deep-level impurities or defects with an activation energy near 0.195 eV. The highest hole mobility(μp=46700cm2/V·s)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$({\\mu _p} = ~46700\\,{\\rm{c}}{{\\rm{m}}^2}\\,/{\\rm{V}}\\cdot{\\rm{s}})$$\\end{document} at 77 K was obtained at the top part, which is moderately compensated. The carrier lifetimes of the grown HPGe crystals were measured using microwave-detected photoconductivity (MDP) at room temperature. The average carrier lifetime decreases from the top to bottom part of the crystal from 130 to 60 µs, which is less than that of the usually observed values in HPGe crystals due to a strong compensation.

Effects of electric polarization and defect energy levels induced by ion irradiation on the electrical behavior of 4H-SiC Schottky barrier diodes

The effects of electric polarization and defect energy levels induced by C4+ irradiation on the electrical behavior of 4H-SiC Schottky barrier diodes (SBDs) are discussed. The parameters of the SBDs were extracted from capacitance–voltage (C–V) and current–voltage (I–V) measurements, the deep level transient spectroscopy (DLTS) was used to identify defect energy levels. In addition, the dielectric function and energy band structure of 4H-SiC were calculated using a first-principles approach to verify the enhancement of polarization and the origin of the defect energy levels. The results show that the net (donor) carrier concentration (N d) increases with the increase of irradiation fluence, which is caused by the competition between irradiation-induced defects and the polarization effect. On the one hand, Z 1/2 is determined by DLTS. It is related to the doubly negatively (2-|0) charged state of V c (carbon vacancy), which is a double acceptor. The intensity of the Z 1/2 peak increases with increasing irradiation fluence, which means that the defects caused by irradiation should reduce the N d. On the other hand, the polarization effect does exist and it becomes stronger with the increase in the irradiation fluence, which makes the N d increase. Obviously, the polarization effect induced by the irradiation is dominant for N d when the depth of ion penetration is in the shallow layer behind the metal–semiconductor (M–S) interface. Irradiation induced electron traps and an uneven distribution of positively charged centers, which can cause ln(I)-V to exhibit a non-linear component before reaching the turn-on voltage. The series resistance (R s), reverse current (I R) increase and the forward current decreases with the increase in irradiation fluence. All these show that the irradiation causes degradation of Ni/4H-SiC SBD performance.

Development of Large‐Diameter and Very High Purity Ge Crystal Growth Technology for Devices (Crystal Research and Technology 5/2023)

Crystal Research and TechnologyVolume 58, Issue 5 2370009 Cover PictureFree Access Development of Large-Diameter and Very High Purity Ge Crystal Growth Technology for Devices (Crystal Research and Technology 5/2023) First published: 12 May 2023 https://doi.org/10.1002/crat.202370009AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Graphical Abstract A 3-inch diameter, 3-kg mass, high-purity germanium crystal is grown with a net free carrier concentration equivalent to one part per trillion and a dislocation density (EPD values) of 103−104 per cm2. Usually, such single crystals with these dimensions are prerequisite to fabricate larger detectors for “rare events” like neutrinoless double beta decay (0νββ) and dark-matter studies to understand the origin and constituents of our Universe. For further details on the growth of this crystal, see article number 2200286 by Rajappan Radhakrishnan Sumathi and co-workers. Volume58, Issue5May 20232370009 RelatedInformation

Development of Large‐Diameter and Very High Purity Ge Crystal Growth Technology for Devices

AbstractHigh‐purity germanium (HPGe) single crystals find their applications as radiation detectors especially for spectroscopy of high‐energy photons and particles in nuclear physics. Growing “detector‐grade” HPGe single crystals, with tailored structural defects and controlled impurity content, uniform throughout the crystal is a challenging task in this type of crystalline semiconductor material. All different process steps for HPGe, namely, i) reducing germanium dioxide powder into Ge metal; ii) zone refining of intrinsic source material (6 N) up to an ultrahigh purity (13 N); iii) Czochralski growth of high‐purity single crystals, are developed in house. A specific preparatory coating process for zone refining is entrenched as part of this work. Gallium, a dominant impurity usually found in HPGe, can be avoided. Using these advanced process know‐hows, a technology to grow volume Ge single crystals of large diameter (3 in.) with very high purity (net carrier concentration ≈ 5 × 1010 cm−3 or equivalent to 1 part per trillion level) is successfully developed. The zone‐refined Ge bars and the crystals show p‐type conductivity. Some crystals exhibit n‐type conductivity, and n–p or p–n transition is encountered in a single growth experiment. Besides the first results of encompassing very high‐purity crystals with uniform diameter, a controlled dislocation density (≈104 cm−2) can be realized.

A simple model for studying the effects of activation treatment on the defects structure of cadmium telluride solar cells

This work presents a SCAPS software model based on defect concentration profiles for the CdTe absorber layer in a CdS/CdTe solar cell. It considers three different phenomena which influence the net free carrier concentration (doping, recombination, and compensation), by assigning them a generic defect level. The model has been successfully tested by simulating JV measurements in dark and light of simple CdS/CdTe devices treated with different CdCl2 and CHClF2-treatments and showing different efficiencies. We found that the obtained defect profiles vary with different treatments as expected, and the results are in good agreement with the literature reports. This indicates that the model may be useful as a simple method for studying and optimizing thin-film solar cells.

Si doping in MOCVD grown (010) β-(AlxGa1−x)2O3 thin films

In this work, the structural and electrical properties of metalorganic chemical vapor deposited Si-doped β-(AlxGa1−x)2O3 thin films grown on (010) β-Ga2O3 substrates are investigated as a function of Al composition. The room temperature Hall mobility of 101 cm2/V s and low temperature peak mobility (T = 65 K) of 1157 cm2/V s at carrier concentrations of 6.56 × 1017 and 2.30 × 1017 cm−3 are measured from 6% Al composition samples, respectively. The quantitative secondary ion mass spectroscopy (SIMS) characterization reveals a strong dependence of Si and other unintentional impurities, such as C, H, and Cl concentrations in β-(AlxGa1−x)2O3 thin films, with different Al compositions. Higher Al compositions in β-(AlxGa1−x)2O3 result in lower net carrier concentrations due to the reduction of Si incorporation efficiency and the increase of C and H impurity levels that act as compensating acceptors in β-(AlxGa1−x)2O3 films. Lowering the growth chamber pressure reduces Si concentrations in β-(AlxGa1−x)2O3 films due to the increase of Al compositions as evidenced by comprehensive SIMS and Hall characterizations. Due to the increase of lattice mismatch between the epifilm and substrate, higher Al compositions lead to cracking in β-(AlxGa1−x)2O3 films grown on β-Ga2O3 substrates. The (100) cleavage plane is identified as a major cracking plane limiting the growth of high-quality Si-doped (010) β-(AlxGa1−x)2O3 films beyond the critical thicknesses, which leads to highly anisotropic and inhomogeneous behaviors in terms of conductivity.

Impact of growth parameters on the background doping of GaN films grown by ammonia and plasma-assisted molecular beam epitaxy for high-voltage vertical power switches

We report on ammonia and plasma-assisted molecular beam epitaxy (NH3-MBE and PAMBE) grown GaN layers with a low net carrier concentration (Nnet). Growth parameters, such as growth rate, V–III ratio, and plasma power, were investigated on different substrates to study their impact on surface morphology and background doping levels using atomic force microscopy and capacitance–voltage (C–V) measurements, respectively. The elevated growth rates are especially interesting for vertical power switches, requiring very thick drift regions (over 10 μm) with low background concentrations. For our NH3-MBE-grown layers, Nnet shows an almost linear increase with the growth rate. Using a freestanding substrate and at a fast growth rate of 1.4 μm hr−1, a Nnet value as low as 1 × 1015 cm−3 was achieved. For samples grown via PAMBE, the lowest Nnet among samples grown under a Ga adlayer was 2 × 1016 cm−3 for a growth rate of 0.32 μm h−1 on a GaN-on-sapphire template. The results support the use of MBE for growing high-quality GaN material with reasonably fast growth rates maintaining low background doping levels for high-voltage vertical power electronic devices.

Influence of alkali element post-deposition treatment on the performance of the CIGS solar cells on flexible stainless steel substrates

In this study, we studied the effect of different alkali element post-deposition treatment (PDT) on the properties of CuInGaSe2 (CIGS) solar cells deposited on flexible stainless steel (SS) substrate. It is found that a certain amount of Na or K is diffused into the surface layer and inside of the CIGS absorption layer by post-deposition treatment process, which can increase the carrier concentration of the absorption layer and effectively improve the material properties of the absorption layer material, thereby improving the open circuit voltage (VOC) and fill factor (FF) of the device. Electron beam-induced current (EBIC) and Capacitance–voltage (C–V)) measurements indicated that the length of the current collection of CIGS absorption layer treated with NaF PDT and NaF + KF PDT is much larger and the total number of net carrier concentration increases significantly. This phenomenon could be attributed to the increase in carrier lifetime after the PDT treatment.

Behavior of Na and RbF‐Treated CdS/Cu(In,Ga)Se2 Solar Cells with Stress Testing under Heat, Light, and Junction Bias

The effects of Na and RbF alkali treatment on the metastability behavior of CdS/Cu(In,Ga)Se2 solar cells are investigated with stress factors of heat, junction bias, and illumination. Four device types with and without Na or RbF treatments are subjected to heat‐ and light‐soaking under open‐ and short‐circuit (OC, SC) junction bias. Low‐Na devices show a higher bandgap due to increased minimum Ga content, higher recombination current, and lower open‐circuit voltage (VOC). Devices with RbF post‐deposition treatment (PDT) show an improvement in net doping density ≈1016 cm−3, VOC, and efficiency. Heat‐ and light‐soaking under OC junction bias provokes an increase in net carrier concentration and VOC irrespective of the alkali treatments. After SC stress, a decrease in VOC and net carrier concentration is observed, which can be stabilized by RbF‐PDT. An increase in Na and oxygen concentration in CIGS is observed for baseline and low‐Na devices, respectively, after OC stress. The oxygen concentration in CdS decreases after heat‐ and light‐soaking for devices without RbF‐PDT, whereas it remains unchanged for devices with RbF‐PDT. The atomic concentration profiles in CIGS significantly stabilize as a function of stress with the addition of RbF‐PDT.

Characterization of high-purity germanium (Ge) crystals for developing novel Ge detectors

High-purity germanium (HPGe) crystals are required to be well-characterized before being fabricated into Ge detectors. The characterization of HPGe crystals is often performed with the Hall Effect system, which measures the net carrier concentration, the Hall mobility, and the electrical resistivity. The reported values have a strong dependence on the size of the ohmic contacts and the geometry of the samples used in conducting the Hall Effect measurements. We conduct a systematic study using four samples cut from the same location in a HPGe crystal made into different sized ohmic contacts or different geometries to study the variation of the measured parameters from the Hall Effect system. The results are compared to the C-V measurements provided by the Ge detector made from the same crystal. We report the systematic errors involved with the Hall Effect system and find a reliable technique that minimizes the systematic error to be only a few percent from the Hall Effect measurements.

Metastable Behavior on Cesium Fluoride‐Treated Cu(In1–x,Gax)Se2 Solar Cells

Metastable behavior of cesium fluoride (CsF)‐treated Cu(In1–x,Gax)Se2 (CIGS) solar cells is investigated under heat‐light soaking (HLS) and heat‐soaking (HS) treatments. HLS increases open‐circuit voltage, fill factor, efficiency, and net carrier concentration and decreases short‐circuit current density, whereas heat‐soaking treatment acts oppositely. The performance of a CsF postdeposition treatment to CIGS thin film in selenium vapor, and closer to stoichiometry copper content, did not mitigate the open‐circuit voltage improvement after HLS. These results argue the traditional concept of the VSe–VCu divacancy complex for the total beneficial effect of HLS in alkali‐treated CIGS solar cells. The metastable behavior observed in the CsF‐treated devices due to the HLS and HS treatments is explained by the specific behavior of alkali‐containing new compounds at the surface and/or the migration of alkali metals at the surface and bulk regions.

Demonstration of a 2 kV Al0.85Ga0.15N Schottky Barrier Diode With Improved On-Current and Ideality Factor

In this letter, we report on demonstrating a Schottky barrier diode (SBD) with high reverse blocking voltage by incorporating an ultra-wide bandgap semiconductor Al0.85 Ga0.15 N channel. Benefited from the lower activation energy of the Si in GaN, the net carrier concentration of Al0.85 Ga0.15N can be essentially enhanced to ${2}\times {10}^{{17}}$ cm−3 level with surface roughness of 0.33 nm. Due to the good material property, a reverse blocking voltage of 2 kV and room temperature ideality factor of 2.3 are demonstrated. Combined with the significantly improved on-current and on/off ratio of more than 106 when compared with other AlN SBDs, Al0.85 Ga0.15 N turns out to be a competitive AlN counterpart by considering the compromise among ultra-wide bandgap, dopant activation, and material property.

Effects of Oxygen Annealing of β-Ga2O3 Epilayers on the Properties of Vertical Schottky Barrier Diodes

Electrical characteristics of vertical Schottky barrier diodes (SBDs) fabricated on as-grown and oxygen annealed β-Ga2O3 (001) epilayers were investigated. SBDs on as-grown epilayer showed anomalous reverse leakage characteristics. Annealing of β-Ga2O3 epilayers in an oxygen-containing environment up to 40 min immensely reduced the reverse leakage current. The specific on-resistance (Ron) of the SBD remained very close to that of the as-grown sample for annealing up to 20 min and increased almost by 25 times for annealing up to 40 min. Simulations of reverse tunneling characteristics, assuming oxygen vacancy type surface states, explained both the magnitude and the shape of anomalous reverse leakage. The diffusion of oxygen during annealing passivated the oxygen vacancy type surface states at first (for 20 min annealing)-resulting in two orders of reduction in leakage with minimal change in Ron. Further annealing (up to 40 min) subsequently reduced the epilayer net carrier concentration from 3.3 × 1016 to 2.9 × 1015 cm−3 -resulting in immense change in both reverse leakage and Ron. Thus, oxygen annealing proved to be a vital technique for the passivation of surface states and to reduce the net carrier concentration, which allows the modulation of reverse leakage of β-Ga2O3 SBDs.

Charge Compensating Defects in Methylammonium Lead Iodide Perovskite Suppressed by Formamidinium Inclusion.

Temperature-dependent photoluminescence (PL) spectroscopy measurements have been performed over a range from 9 K to room temperature on polycrystalline methylammonium (MA)/formamidinium (FA) lead iodide (MA1-xFAxPbI3) perovskite thin films. Our low-temperature PL analysis reveals the existence of charge compensating defects in MAPbI3, which may explain the lower net free carrier concentration in MAPbI3 perovskite. More interestingly, we observe the suppression of the PL emission associated with the charged defects by appropriate FA inclusion. Furthermore, FA incorporation into MAPbI3 has been found to slow the phase transformation of MA1-xFAxPbI3 from orthorhombic to tetragonal phase, which occurs with increasing temperature. Our analyses of the FA concentration's impact on defect density and structural phase transformation provide beneficial insights that improve the understanding of the photovoltaic properties and application of organic-inorganic metal halide perovskites.

Proton Irradiation on Cesium‐Fluoride‐Free and Cesium‐Fluoride‐Treated Cu(In,Ga)Se2 Solar Cells and Annealing Effects under Illumination

Several studies have been performed on proton irradiation onto alkali‐metal untreated Cu(In,Ga)Se2 (CIGS) solar cells. However, there are almost no studies describing similar effects on alkali‐treated CIGS solar cells. With this motivation, this work investigates proton irradiation and annealing effects under illumination on cesium‐fluoride‐free (CsF‐free) and CsF‐treated CIGS solar cells. Both CsF‐free and CsF‐treated CIGS solar cells degrade under proton irradiation. External quantum efficiency measurements show degradation in long wavelengths after the treatment. The experimental data are fitted with a simulation, which show that proton‐irradiated degradation is more severe at high fluence. Capacitance–voltage measurements show a broadening of the depletion region after proton irradiation, which is due to the decreased net carrier concentration. It is proposed that proton irradiation at low fluence generates shallow‐type defects, whereas high‐fluence protons generate deep defects. However, it is observed that room‐temperature storage of the proton‐irradiated solar cells causes partial recovery. Thermal annealing under illumination treatments is found to be beneficial to the drastic recovery of the performance of solar cells irradiated at low fluence. High‐fluence proton‐irradiated solar cells undergo minor recovery.

(Invited) Effects of Annealing Capped (0001) Oriented GaN Samples

Changes in the topological, structural, electrical and optical properties produced by annealing (0001) oriented GaN homo- and hetero- epitaxial films that were protected by an AlN cap and annealed at a temperature, TA, ranging from 1150 to 1300 ºC for a time, t A, ranging from 1 to 8 min are discussed. The films were as-grown or Mg implanted unintentionally doped n-type, or they were Mg doped. For as-grown hetero-epitaxial films the step-flow growth patterns on the as-grown surface survive up to TA ≤ 1300 ºC and t A ≤ 2 min. Small angle grain boundaries parallel to the {1100} M-planes become more defined on the surface of the hetero-structure films as TA and/or t A increases so long as it retains its smooth step-flow growth pattern. Small hexagonal etch pits associated with threading edge dislocations decorate these boundaries suggesting that the grain boundaries are created by polygonization. These boundaries are present in the as-grown film, but they do evolve over time at different rates at different temperatures as is illustrated in the (00.2), (10.2), (30.2) x-ray rocking curves, (10.5) ω - 2θ scans, and reciprocal space maps. Similar studies of films grown on ammonothermal bulk single crystals show similar trends, but they are much more muted. All of these studies require an annealing cap to minimize the rate of preferential evaporation of nitrogen. The GaN surface must be clean and smooth, the cap must adhere well, and one must be able to preferentially etch it off after the anneal. A thin AlN film grown epitaxially by MOCVD at low temperatures combined with a thicker sputtered AlN film meets all of these requirements, but it only does so up TA = 1300 ºC for t A < 8 min. It fails at higher TA because the N vapor pressure at 1300 ºC is about equal to the yield stress of AlN. Our caps fail when t A > 8 min at TA 1300 ºC because even some N escapes with a good seal. When the cap does not seal as well, the GaN film decomposes first at the small angle grain boundaries. Even when the surface of the film is smooth, the electrical properties show that the anneal has altered the internal structure. The conductance above the voltage knee of Schotty diodes fabricated on them initially increases with TA and t A, but it begins to drop off at TA = 1200 or 1250 ºC suggesting that at lower TA some of the structural defects are annealed out thereby increasing the mobility, but at higher TA other types of defects, possibly nitrogen vacancy, NV, complexes are created. This explanation is consistent with the observation of the conductance below the voltage knee being larger at the larger TA because the tunneling current through the defects associated with the NV is larger. The reverse leakage current follows the same trend – it being larger at the larger TA. The CV characteristics of the diode suggests that this defect layer is mostly confined to the region near the surface as the net carrier concentration as measured at the end of the depletion layer does not change with TA until TA ≥ 1250 ºC when the defected area is at the end of the depletion layer at zero bias. Defects of a different nature are created by the implant process as determined by the increased breadth of the XRD curves and the creation of another peak. But much of that damage is annealed out as the peak widths return to almost their original breadth and the second peak disappears. However, they do not return to their original breadth. It is not clear whether this is due to not removing all of the implant damage or the damage created by the annealing process contributing to the increased breadth. We are now in the process of deciphering the more complicated electrical measurements made on the Mg implanted or doped samples, and expect to report on them at the meeting.

The further investigation of N-doped β-Ga2O3 thin films with native defects for Schottky-barrier diode

The structural, electronic and optical properties of β-Ga2O3 thin films with different N ion concentrations are investigated. With N concentrations increasing, the crystallization degrades and even polycrystalline appears. After Ar annealing treatment, the crystallization of N-doped β-Ga2O3 thin films improved owing to recovery of the implantation-damaged crystals. The N-doped Ga2O3 thin films were used to construct vertical Schottky diodes comprising Ga2O3:N/n-Ga2O3. The net carrier concentrations of these devices degrade one-two orders due to the compensation effect of more N implantation, which suggests that hole could be mobile although N is a deep acceptor dopant. The phenomenon could be explained by the decrease of the ionization energy of N dopant due to the complex defects NGa2O3VO (N-doped β-Ga2O3 with O vacancy) and NGa2O3VGa (N-doped β-Ga2O3 with Ga vacancy). Thus, the development of N ion implantation for β-Ga2O3 has its potential opportunity for β-Ga2O3 power devices.