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Han, Jung

Publications and source records attributed to Han, Jung.

13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Comparison of Mg-based liquid metal ion sources for scalable focused-ion-implantation doping of GaN

We compare the suitability of various magnesium-based liquid metal alloy ion sources (LMAISs) for scalable focused-ion-beam (FIB) implantation doping of GaN. We consider GaMg, MgSO 4 $\bullet$7H 2 O, MgZn, AlMg, and AuMgSi alloys. Although issues of oxidation (GaMg), decomposition (MgSO 4 $\bullet$7H 2 O), and excessive vapor pressure (MgZn and AlMg) were encountered, the AuMgSi alloy LMAIS operating in a Wien-filtered FIB column emits all Mg isotopes in singly and doubly charged ionization states. We discuss the operating conditions to achieve <20 nm spot size Mg FIB implantation and present Mg depth profile data from time-of-flight secondary ion mass spectrometry. We also provide insight into implantation damage and recovery based on cathodoluminescence spectroscopy before and after rapid thermal processing. Prospects for incorporating the Mg LMAIS into high-power electronic device fabrication are also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Regrowth and Selective Area Growth of GaN for Vertical Power Electronics

Gallium Nitride (GaN) has a great potential in high-power and high-frequency applications due to its wide energy gap and good transport property. So far all commercial GaN optoelectronic and electronic devices have planar junctions and heterostructures prepared by epitaxial growth. To take the advantage of the merits of GaN material properties, more sophisticated device configurations such as current-aperture vertical electron transistors (CAVETs), junction field-effect transistors (JFETs), and super-junction (SJ) devices require the ability to form in-plane, lateral junctions by selective area doping (SAD). In this project, we explored a novel approach of realizing SAD through selective-area etching (SAE) followed by selective-area growth (SAG).

36 MATERIALS SCIENCE↗
DOE OSTI2022

Unveiling the influence of selective-area-regrowth interfaces on local electronic properties of GaN p-n junctions for efficient power devices

Here, we report correlated nanoscale mapping of the structure, composition, and properties of regrown GaN p-n junctions to identify how etching and non-planar regrowth processes limit diode performance via the introduction of unintentional dopants and defect states. p-GaN was selectively regrown in n-GaN trenches with SiO 2 masks of variable mask-to-trench-width ratio. Dilute Al layers were periodically introduced during regrowth as markers of the growth interface. Correlated nanoscale mapping of doping, conductivity, and dopant complexes was achieved with atom probe tomography (APT), scanning spreading resistance microscopy (SSRM), and cathodoluminescence (CL) spectroscopy, respectively. The Al marker layers, detected by APT, enabled reconstruction of the faceted growth interface and correlation of the dopant concentration with position and time. The p-GaN growth rate is proportional to the mask-to-trench width ratio while the dopant incorporation rate is invariant. At trench edges, magnesium incorporation is suppressed, and oxygen incorporation enhanced, due to preferential incorporation on the semi-polar growth surface, leading to compensation and less abrupt p-n junctions; the SiO 2 mask is a source of oxygen. Residual etch damage below the regrowth interface induces n-type and p-type conductivity, creating leakage pathways. The non-uniform Mg incorporation is driven by crystal anisotropy and is thus inherent to non-planar regrowth, but can be mitigated by engineering the regrowth interface and process parameters. The unprecedented integration of spatially resolved mapping of dopants, impurities, conductivity, and carrier type is a powerful approach to discriminating distinct factors that limit the performance of regrown diodes, enabling the rational optimization of process and device design.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Etched-And-Regrown GaN P–N Diodes with Low-Defect Interfaces Prepared by In Situ TBCl Etching

The ability to form pristine interfaces after etching and regrowth of GaN is a prerequisite for epitaxial selective area doping, which in turn is needed for the formation of lateral PN junctions and advanced device architectures. In this work, we report the electrical properties of etched-and-regrown GaN PN diodes using an in situ Cl-based precursor, tertiary butylchloride (TBCl). We demonstrated a regrowth diode with I–V characteristics approaching that from a continuously grown reference diode. The sources of unintentional contamination from the silicon (Si) impurity and the mediating effect of Si during the TBCl etching are also investigated in this study. Furthermore, this work points to the potential of in situ TBCl etching toward the realization of GaN lateral PN junctions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

X-ray topography characterization of gallium nitride substrates for power device development

Gallium nitride substrates grown by the hydride vapor phase epitaxy (HVPE) method using a patterned growth process have been characterized by synchrotron monochromatic beam X-ray topography in the grazing incidence geometry. Images reveal a starkly heterogeneous distribution of dislocations with areas as large as 0 3 mm 2 containing threading dislocation densities below 10 3 cm -2 in between a grid of strain centers with higher threading dislocation densities (> 10 4 cm -2 ). Basal plane dislocation densities in these areas are as low as 104 cm -2 . By comparing the recorded images of dislocations with ray tracing simulations of expected dislocations in GaN, the Burgers vectors of the dislocations have been determined. The distribution of threading screw/mixed dislocations (TSDs/TMDs), threading edge dislocations (TEDs) and basal plane dislocations (BPDs) is discussed with implications for fabrication of power devices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

A study of damage-free in-situ etching of GaN in metalorganic chemical vapor deposition (MOCVD) by tertiarybutylchloride (TBCl)

This paper reports a study of the effect of NH 3 flow rate and reactor temperature on the tertiarybutylchloride (TBCl) etching of patterned GaN-on-sapphire templates. It is found that a reduced NH 3 flow rate and an elevated reactor temperature can eliminate islands or dots on the surface, while at the same time, enhance the etching around dislocations. TBCl etching was also performed on planar bulk GaN templates with much lower dislocation density. We find an atomically flat and layer-by-layer etching behavior within the region free of dislocations. Surface kinetics analysis reveals a short diffusion length of etching products. Room-temperature photoluminescence (PL) and x-ray photoelectron spectroscopy (XPS) measurements confirm that TBCl etching is capable of removing the damage and impurities induced by plasma etching without introducing additional damage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Conductivity based on selective etch for GaN devices and applications thereof

This invention relates to methods of generating NP gallium nitride (GaN) across large areas (>1 cm2) with controlled pore diameters, pore density, and porosity. Also disclosed are methods of generating novel optoelectronic devices based on porous GaN. Additionally a layer transfer scheme to separate and create free-standing crystalline GaN thin layers is disclosed that enables a new device manufacturing paradigm involving substrate recycling. Other disclosed embodiments of this invention relate to fabrication of GaN based nanocrystals and the use of NP GaN electrodes for electrolysis, water splitting, or photosynthetic process applications.

Zhang, Yu↗
DOE OSTI2019

In situ and selective area etching of GaN by tertiarybutylchloride (TBCl)

In situ etching (ISE) of gallium nitride (GaN) can enable lateral and vertical junctions through selective area etching (SAE) and regrowth. We report the study of ISE and SAE of GaN using an organometallic precursor, tertiarybutylchloride (TBCl), in a metal-organic chemical vapor deposition reactor. Compared to the conventional etching in hydrogen, the use of TBCl allows in situ etching at a much lower temperature (<850 °C), likely due to a more reactive etchant and a more efficient desorption rate of the etching products. The TBCl etching is near equilibrium and can be significantly changed with the change of the NH3 flow rate. We also report initial results of SAE on SiO 2 patterned GaN samples. An important finding is the need to control the desorption of the reaction products in order to achieve smooth surfaces. TBCl etching is crystallographically anisotropic with low etch rates on N-terminated facets. The use of TBCl and possibly other organometallic halogen precursors is expected to enable the design and implementation of III-nitride lateral junction devices that have not been possible.

42 ENGINEERING↗
DOE OSTI2019

Heterogeneous material integration through guided lateral growth

Methods are provided for generating a crystalline material. The methods comprise depositing a textured thin film in a growth seed area, wherein the textured thin film has a preferential crystallographic axis; providing a growth channel extending from the growth seed area, the growth channel permitting guided lateral growth; and growing a crystalline material in the growth channel along a direction that is substantially perpendicular to the preferential crystallographic axis of the textured thin film. A preferred crystalline material is gallium nitride, and preferred textured thin films are aluminum nitride and titanium nitride.

Han, Jung↗
DOE OSTI2019

Nanoscale selective growth and microstructural control of indium nitride (InN)

Selective area growth (SAG) is a phenomenon in thin film deposition where the sample surface is masked by a dielectric or refractory layer such that growth takes place only in the exposed window regions. As the opening window is pushed to nano-scale, it becomes possible to confine and control epitaxial evolution with lithographically engineered geometry with a feature size comparable to that ofa single nucleus. Two fundamental questions in nano-scale SAG are studied. The first one is how does nano-scale constriction in one direction impact the microstructure evolution in the other orthogonal directions. The other question is how does the presence of nano-scale geometric boundaries affect the crystallographic orientation in selective area epitaxy? InN is chosen as a case study to demonstrate the efficacy and unveil the science in nano-scale SAG. For the first time, we achieve uniform InN nanowires in the large scale with nano-trenches. The engineering of InN nuclei with interfacial energy and the possibility of orientation filtering are also studied.

36 MATERIALS SCIENCE↗