Proton irradiation effects on minority carrier diffusion length and defect introduction in homoepitaxial and heteroepitaxial n-GaN

Collins, Kimberly; Armstrong, Andrew M.; Allerman, Andrew A.; Vizkelethy, György; Deusen, Stuart B. Van; Léonard, François; Talin, A. Alec

doi:10.1063/1.5006814

Cited by 20 publications

(7 citation statements)

References 37 publications

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“…2b. Initial measurements show the minority carrier length for n-type GaN to be 265 ± 27 nm, which is consistent with reported values for these samples [4]. We will present further measurements of in situ reverse biasing and subsequent changes in EBIC signals.…”

supporting

confidence: 85%

Measuring the minority carrier diffusion length in n-GaN using bulk STEM EBIC

et al. 2018

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Gallium nitride is currently being investigated for demanding applications such as high-temperature and high-power electronics as well as space-based or other high radiation exposure applications. It has a wide bandgap and is more resistant than Si to high fluxes of proton and electron radiation [1]. Electron irradiation of GaN is believed to create both N and Ga vacancies, as well as to induce threading dislocation glide. These defects can act as recombination centers which reduce the overall minority carrier lifetime and mobility. Measurements of the minority carrier diffusion length in GaN can be studied using cathodoluminescence (CL) or electron beam induced current (EBIC) in a scanning electron microscope (SEM). However, as recently reported in Yakimov et. al. [2], the EBIC planar geometry in SEM often leads to an over estimation of the minority carrier diffusion length in n-type GaN. This over estimation is attributed to the interaction volume in SEM, which is on the order of hundreds of nanometers to a few microns and overlaps with the measured minority carrier diffusion length of n-GaN, reported to be between a few tens of nanometers to a few microns [2].Here we report on scanning transmission electron microscopy (STEM) EBIC characterization of Schottky diodes consisting of hydride vapor phase epitaxy (HPVE) grown n-GaN and patterned Ni contacts. We demonstrate that by using a bulk STEM EBIC technique, the minority carrier diffusion length, Ld, can be separated from the interaction volume diameter, R. An accelerating voltage of 100 kV or 200 kV in STEM gives a much larger interaction volume than an accelerating voltage of 5 to 30 kV does in SEM. We have shown previously [3] that the interaction volume is approx. 4 µm for 100 kV and 14 µm for 200 kV, which are both much larger than the expected diffusion length, Ld for n-type GaN. Since the length scales for R and Ld are quite different, we can separate the exponential decay of the interaction volume from the exponential decay of the diffusion length. This allows accurate measurement of diffusion lengths in a convenient planar geometry while avoiding the pitfalls of planar geometry in SEM EBIC.Our sample consists of a high purity single crystal n-type GaN substrate (275 µm thick) grown by HVPE with a threading dislocation density of ~10 6 /cm 2 and patterned with a nickel Schottky contact as well as an indium ohmic contact. As can be seen in Fig. 1b, the GaN sample is patterned with a Ni contact and wired with Ag epoxy to an Au wire. Since the EBIC image only shows areas where charge carriers are measurably excited and separated, only the Ni pad and some of the Ag epoxy is visible. Fig. 2a shows the line profile EBIC signal as a function of distance, which was taken from the inset of 2a. As can be seen, is a short, fast decay and a long, slow decay. These two exponential decays can be fit and two different decay lengths can be solved for, shown in Fig. 2b. Initial measurements show the minority carrier length for n-type GaN to be 265 ± 27 nm, which is co...

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confidence: 85%

Measuring the minority carrier diffusion length in n-GaN using bulk STEM EBIC

et al. 2018

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“…The DLTS and DLOS spectra are shown in Figure a,b, respectively. Common impurities in GaN that compensate n‐type doping are C, Fe, and Mg. Zhang et al [ 43,44 ] showed that the E C ‐1.3 eV and E C ‐3.28 eV deep levels, which are most likely C i and C N , respectively, [ 21,45,46 ] are the carbon‐related traps primarily responsible for producing compensated GaN. Fe forms a level at E C ‐0.57 eV that compensates the n‐type doping.…”

Section: Resultsmentioning

confidence: 99%

“…We note here that the DLTS/DLOS results on these samples reveal comparable low trap concentrations with state‐of‐the‐art GaN MOCVD reports for high power vertical device applications. [ 36,46,52–55 ]…”

Section: Resultsmentioning

confidence: 99%

Metalorganic Chemical Vapor Deposition Gallium Nitride with Fast Growth Rate for Vertical Power Device Applications

Zhang

Chen

et al. 2021

Physica Status Solidi (a)

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The development of high‐quality gallium nitride (GaN) epitaxy with thick drift layer, low controllable doping, and high mobility is key for vertical high‐power devices. Herein, the effect of increasing trimethylgallium (TMGa) molar flow rate on the growth rate, impurity incorporation, charge compensation, surface morphology, and carrier mobility is systematically studied. An optimized metalorganic chemical vapor deposition GaN growth condition with a typical growth rate of 2 μm h−1 is used as the baseline. With significant suppression of background Si, other impurity concentrations, and a precise control of the doping precursor SiH4 flow, an electron concentration as low as 4 × 1015 cm−3 in n−‐GaN is achieved. Through increasing the TMGa flow rate, the GaN growth rate is increased to 5.2 μm h−1. Secondary ion mass spectroscopy results show that the background H, O, and Mg remain below detection limit, but C level is increased to 2 × 1016 cm−3. GaN growth on Mn‐doped semi‐insulating GaN substrate is performed to probe the transport properties of film with low dislocation densities. Hall measurement shows that an electron mobility decreases from 852 to 604 cm2 V−1 s−1 as the growth rate increases. Results from this work reveal the challenge and guidance for achieving GaN vertical high power devices.

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“…GaN-based materials are ideal materials for manufacturing electronic devices with high-voltage, high-temperature and high-frequency applications, due to its superior comprehensive performances; another feature of GaN-based heterostructures and devices is that they have the potential capability to exhibit extremely high radiation hardness. So, GaN-based devices will be a better candidates for applications in outer space and other radiation environment [1,2], where the devices have to operate reliably when subjected to irradiations of protons, γ-rays, or neutrons. There had been considerable effort to understand the nature of radiation defects in GaN-based heterostructures [3][4][5].…”

Section: Introductionmentioning

confidence: 99%

Study on Neutron Irradiation-Induced Structural Defects of GaN-Based Heterostructures

Lin

et al. 2018

Crystals

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The GaN-based heterostructures and related HEMTs (High Electron Mobility Transistors) were investigated by 1MeV neutrons at fluences up to 10 15 cm −2 , yielding an increase of the densities of screw dislocations and edge dislocations for GaN-based heterostructures. It gave the result that neutron irradiation-induced structural defects into GaN-based materials, and the irradiation-induced dislocations would propagate to the material surface causing surface morphology deterioration. However, the GaN-based material strain was robust to neutrons, and the more initial dislocations, the easier to generate irradiation defects and thus, more strongly affecting the electrical property degradations of materials and devices. Meanwhile, the reduction of the two-dimensional electron gas (2DEG) concentration (n s) caused by irradiation-induced defects led to the reducing the drain current. Moreover, the significant degradation of the reverse gate leakage current at fluences ranging from 10 14 to 10 15 cm −2 could be attributed to the irradiation-induced deep defects. The neutron induced damage was more difficult to anneal recovery than other particles, due to the neutron irradiation-induced deep levels and defect complexes such as defect clusters.

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Proton irradiation effects on minority carrier diffusion length and defect introduction in homoepitaxial and heteroepitaxial n-GaN

Cited by 20 publications

References 37 publications

Measuring the minority carrier diffusion length in n-GaN using bulk STEM EBIC

Measuring the minority carrier diffusion length in n-GaN using bulk STEM EBIC

Metalorganic Chemical Vapor Deposition Gallium Nitride with Fast Growth Rate for Vertical Power Device Applications

Study on Neutron Irradiation-Induced Structural Defects of GaN-Based Heterostructures

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