arXiv subjects

Jung-Hun Seo

Publications and source records attributed to Jung-Hun Seo.

15 recordsLinked to original sources

arXiv2026

Band alignment of grafted diamond/GaN p-n heterojunctions interfaced with ALD Al2O3 and SiNx/Al2O3

Diamond and gallium nitride are complementary semiconductors for forming p-n junctions because of their respective doping limitations. Understanding the band alignment of grafted diamond/GaN heterojunctions is therefore essential for optimizing diode performance. In this study, the band alignment of diamond/Al2O3/GaN and diamond/Al2O3/SiNx/GaN heterostructures was determined by X-ray photoelectron spectroscopy. Both structures exhibit type-II band alignment, but with different band offsets. The band offsets of the diamond/Al2O3/SiNx/GaN heterojunction are larger by 0.42 eV than those of diamond/Al2O3/GaN. This difference is attributed to a modification of the interfacial electrostatic potential, which may arise from a reduced density of positive fixed charges in the interfacial dielectric near the diamond/Al2O3 interface after insertion of the SiNx layer. These results demonstrate that interfacial-layer engineering provides an effective strategy for tailoring the band alignment of grafted diamond/GaN heterojunctions, offering guidance for the design of p-n diodes with tunable rectifying characteristics.

cond-mat.mtrl-sci↗

arXiv2025

Preliminary Demonstration of Diamond-GaN pn Diodes via Grafting

Ultrawide bandgap (UWBG) semiconductors exhibit exceptional electrical and thermal properties, offering strong potential for high power and high frequency electronics. However, efficient doping in UWBG materials is typically limited to either n type or p type, constraining their application to unipolar devices. The realization of pn junctions through heterogeneous integration of complementary UWBG or WBG semiconductors is hindered by lattice mismatch and thermal expansion differences. Here, we report the preliminary demonstration of diamond GaN heterojunction pn diodes fabricated via grafting. A single crystalline p plus diamond nanomembrane was integrated onto an epitaxially grown c plane n plus GaN substrate with an ultrathin ALD Al2O3 interlayer. The resulting diodes exhibit an ideality factor of 1.55 and a rectification ratio of over 1e4. Structural and interfacial properties were examined by AFM, XRD, Raman, and STEM, providing critical insights to guide further optimization of diamond GaN pn heterojunction devices.

cond-mat.mtrl-sci↗

arXiv2024

XPS analysis of molecular contamination and sp2 amorphous carbon on oxidized (100) diamond

The efficacy of oxygen (O) surface terminations on diamond is an important factor for the performance and stability for diamond-based quantum sensors and electronics. Given the wide breadth of O-termination techniques, it can be difficult to discern which method would yield the highest and most consistent O coverage. Furthermore, the interpretation of surface characterization techniques is complicated by surface morphology and purity, which if not accounted for will yield inconsistent determination of the oxygen coverage. We present a comprehensive approach to consistently prepare and analyze oxygen termination of surfaces on (100) single-crystalline diamond. We report on X-ray Photoelectron Spectroscopy (XPS) characterization of diamond surfaces treated with six oxidation methods that include various wet chemical oxidation techniques, photochemical oxidation with UV illumination, and steam oxidation using atomic layer deposition (ALD). Our analysis entails a rigorous XPS peak-fitting procedure for measuring the functionalization of O-terminated diamond. The findings herein have provided molecular-level insights on oxidized surfaces in (100) diamond, including the demonstration of clear correlation between the measured oxygen atomic percentage and the presence of molecular contaminants containing nitrogen, silicon, and sulfur. We also provide a comparison of the sp2 carbon content with the O1s atomic percentage and discern a correlation with the diamond samples treated with dry oxidation which eventually tapers off at a max O1s atomic percentage value of 7.09 +/- 0.40%. Given these results, we conclude that the dry oxidation methods yield some of the highest oxygen amounts, with the ALD water vapor technique proving to be the cleanest technique out of all the oxidation methods explored in this work.

cond-mat.mtrl-sci↗

arXiv2022

Transient Characteristics of $β$-Ga$_2$O$_3$ Nanomembrane Schottky Barrier Diodes on Various Substrates

In this paper, a transient delayed rising and fall time of $β$-Ga$_2$O$_3$ NMs Schottky barrier diodes (SBDs) formed on four different substrates (diamond, Si, sapphire, and polyimide) were measured using a sub-micron second resolution time-resolved electrical measurement system under a different temperature condition. The devices exhibited noticeably less-delayed turn-on-/off- the transient time when $β$-Ga$_2$O$_3$ NMs SBDs were transfer-printed on a high-k substrate. Furthermore, a relationship between the $β$-Ga$_2$O$_3$ NM thicknesses and their transient characteristics were systematically investigated and found that phonon scattering plays an important role in heat dissipation as the thickness of $β$-Ga$_2$O$_3$ NMs get thinner which is also verified by the Multiphysics simulator. Overall, our result reveals the impact of various substrates with different thermal properties and different \b{eta}- Ga2O3 NMs thickness with the performance of $β$-Ga$_2$O$_3$ NMs based devices. Hence, these results can guide further efforts us to optimize the performance of future $β$-Ga$_2$O$_3$ devices by maximizing heat dissipation from the $β$-Ga$_2$O$_3$ layer.

physics.app-ph↗

arXiv2021

Electrical and Thermal Property of Si/GaAs Heterojunction Formed by Ultra-Thin Oxide Interfacial Layer

We have successfully demonstrated Si/GaAs p-n heterostructures using Al2O3 ultra-thin oxide interfacial layers. The band diagram and band offsets were investigated using X-ray photoelectron spectroscopy and confirm a small discontinuity in the conduction band (0.03 eV) at the interface. The interface defect density (Dit) values of the heterointerface with different ultra-thin oxide (UO) thicknesses ranged from 0.35 nm to 3.5 nm and were also characterized based on a metal-oxide-semiconductor capacitor (MOSCAP) structure using a capacitance-voltage measurement. The results revealed that a thin UO interfacial layer (around 1 nm) maximizes carrier transport property due to better surface passivation and efficient tunneling properties. Thermal property investigation also shows that the Al2O3 UO interfacial layer offers a good tunneling layer but also facilitates phonon transport across the interface. Finally, the electrical characterization of Si/GaAs heterojunction p-n diodes confirms reliable rectifying behavior with an extremely low ideality factor; thus, heterogeneous integration using the UO approach offers a robust way to create more types of heterojunctions between dissimilar semiconductors.

cond-mat.mtrl-sci↗

arXiv2021

Investigation of the Imperfect Interface at the Si/GaAs Heterojunction Formed by Ultra-Thin Oxide Interfacial Layer

The structure property of non-ideal Si/GaAs heterostructures that were integrated with the ultra-thin oxide (UO) tunneling interfacial layer has been systematically investigated. Si nanomembranes (NMs) were oxidized in different time periods prior to the hetero-integration process to create the non-ideal single-side passivated Si/GaAs heterostructure. The atomic level oxygen distribution and the degree of oxygen content in Si NM and GaAs were carefully investigated using the atom probe tomography (APT) and X-ray photoelectron spectroscopy (XPS) to trace the changes in chemical composition and reactional mechanism across the UO interface when the surface of Si NM was exposed to air for different period of time. The negatively induced charges at the UO layer caused the oxygen diffusion to GaAs layer and formed the unwanted GaAs oxide layer. This native oxide stack noticeably degraded the thermal properties of the Si/GaAs heterostructure as Si NMs were more oxidized. This study revealed that the poor surface passivation on the one side of the heterointerface leads to a both-side oxidation, thus severely deteriorating the transport properties across the heterojunction that is formed with the UO layer.

cond-mat.mtrl-sci↗

arXiv2021

Theoretical Prediction of Heterogeneous Integration of Dissimilar Semiconductor with Various Ultra-Thin Oxides and 2D Materials

In this paper, we have built a numerical p-n Si/GaAs heterojunction model using a quantum-mechanical tunneling theory with various quantum tunneling interfacial materials including two-dimensional semiconductors such as hexagonal boron nitride (h-BN) and graphene and ALD-enabled oxide materials such as HfO2, Al2O3, and SiO2. Their tunneling efficiencies and tunneling current with different thicknesses were systematically calculated and compared. Multiphysics modeling was used with the aforementioned tunneling interfacial materials to analyze changes in strain under different temperature conditions. Considering the transport properties and thermal-induced strain analysis, Al2O3 among three oxide materials and graphene in 2D materials are favorable material choices that offer the highest heterojunction quality. Overall, our results offer the viable route to guide the selection of quantum tunneling materials for myriad possible combinations of new heterostructures that can be obtained via remote epitaxy and the UO method.

cond-mat.mes-hall↗

arXiv2021

Chalcogenide perovskite BaZrS3 thin-film electronic and optoelectronic devices by low temperature processing

Owing to its superior visible light absorption and high chemical stability, chalcogenide perovskite barium zirconium sulfide has attracted significant attention in the past few years as a potential alternative to hybrid halide perovskites for optoelectronics. However, the high processing temperatures of BaZrS3 thin films at above 1000 C severely limits their potential for device applications. Herein, we report the synthesis of BaZrS3 thin films at temperatures as low as 500 C, by changing the chemical reaction pathway. The single phase BaZrS3 thin film was confirmed by X-ray diffraction and Raman spectroscopies. Atomic force microscopy and scanning electron microscopy show that crystalline size and surface roughness were consistently reduced with decreasing annealing temperature. The lower temperatures further eliminate sulfur vacancies and carbon contaminations associated with high temperature processing. The ability to synthesize chalcogenide perovskite thin films at lower temperatures removes a major hurdle for their device fabrication. The photodetectors demonstrate fast response and an on/off ratio of 80. The fabricated field effect transistors show an ambipolar behavior with electron and hole mobilities of 16.8 cm2/Vs and 2.6 cm2/Vs, respectively.

cond-mat.mtrl-sci↗

arXiv2021

Large-Size Free-Standing Single-crystal b-Ga2O3 Membranes Fabricated by Hydrogen Implantation and Lift-Off

In this paper, we have demonstrated the large-size free-standing single-crystal b-Ga2O3 NMs fabricated by the hydrogen implantation and lift-off process directly from MOCVD grown b-Ga2O3 epifilms on native substrates. The optimum implantation conditions were simulated with a Monte-Carlo simulation to obtain the high hydrogen concentration with a narrow ion distribution at the desired depth. Two as grown b-Ga2O3 samples with different orientation ([100] and [001]) were used and successfully create 1.2 um thick b-Ga2O3 NMs without any physical damages. These b-Ga2O3 NMs were then transfer-printed onto rigid and flexible substrates such as SiC substrate and polyimide substrate. Various material characterizations were performed to investigate the crystal quality, surface morphology, optical property, mechanical property, and bandgap before and after the lift-off and revealed that good material quality is maintained. This result offers several benefits in that the thickness, doping, and size of b-Ga2O3 NMs can be fully controlled. Moreover, more advanced b-Ga2O3-based NM structures such as (AlxGa1-x)2O3/Ga2O3 heterostructure NMs can be directly created from their bulk epitaxy substrates thus this result provides a viable route for the realization of high performance b-Ga2O3 NM-based electronics and optoelectronics that can be built on various substrates and platforms.

cond-mat.mtrl-sci↗

arXiv2018

Lattice-mismatched semiconductor heterostructures

Semiconductor heterostructure is a critical building block for modern semiconductor devices. However, forming semiconductor heterostructures of lattice-mismatch has been a great challenge for several decades. Epitaxial growth is infeasible to form abrupt heterostructures with large lattice-mismatch while mechanical-thermal bonding results in a high density of interface defects and therefore severely limits device applications. Here we show an ultra-thin oxide-interfaced approach for the successful formation of lattice-mismatched semiconductor heterostructures. Following the depiction of a theory on the role of interface oxide in forming the heterostructures, we describe experimental demonstrations of Ge/Si (diamond lattices), Si/GaAs (zinc blende lattice), GaAs/GaN (hexagon lattice), and Si/GaN heterostructures. Extraordinary electrical performances in terms of ideality factor, current on/off ratio, and reverse breakdown voltage are measured from p-n diodes fabricated from the four types of heterostructures, significantly outperforming diodes derived from other methods. Our demonstrations indicate the versatility of the ultra-thin-oxide-interface approach in forming lattice-mismatched heterostructures, open up a much larger possibility for material combinations for heterostructures, and pave the way toward broader applications in electronic and optoelectronic realms.

physics.app-ph↗

arXiv2017

229 nm UV LEDs using p-type silicon for increased hole injection

Ultraviolet (UV) light emission at 229 nm wavelength from diode structures based on AlN/Al0.77Ga0.23N quantum wells and using p-type Si to significantly increase hole injection was reported. Both electrical and optical characteristics were measured. Owing to the large concentration of holes from p-Si and efficient hole injection, no efficiency droop was observed up to a current density of 76 A/cm2 under continuous wave operation and without external thermal management. An optical output power of 160 uW was obtained with corresponding external quantum efficiency of 0.027%. This study demonstrates that by adopting p-type Si nanomembrane contacts as hole injector, practical levels of hole injection can be realized in UV light-emitting diodes with very high Al composition AlGaN quantum wells, enabling emission wavelengths and power levels that were previously inaccessible using traditional p-i-n structures with poor hole injection efficiency.

physics.app-ph↗

arXiv2017

UVC LEDs on Bulk AlN Substrates Using Silicon Nanomembranes for Efficient Hole Injection

As UV LEDs are explored at shorter wavelengths (< 280 nm) into the UVC spectral range, the crystalline quality of epitaxial AlGaN films with high Al compositions and inefficient hole injection from p-type AlGaN severely limit the LED performance and development. In this work, we report on 237 nm light emission with a record light output power of 265 uW from AlN/Al0.72Ga028N multiple quantum well UVC LEDs using bulk AlN substrates and p-type silicon nanomembrane contact layers for significantly improved AlGaN film quality and hole injection, respectively. No intensity degradation or efficiency droop was observed up to a current density of 245 A/cm2, which is attributed to the low dislocation density within AlGaN films, the large concentration of holes from p-Si, and efficient hole-transport to the active region. Additionally, the emission peak at 237 nm is dominant across the electroluminescence spectrum with no significant parasitic emissions observed. This study demonstrates the feasibility of using p-Si as a hole injector for UVC LEDs, which can be extended to even shorter wavelengths where hole injection from chemically doped AlGaN layers is not feasible.

physics.app-ph↗

arXiv2016

Thermal Diffusion Boron Doping of Single-Crystal Diamond

With the best overall electronic and thermal properties, single crystal diamond (SCD) is the extreme wide bandgap material that is expected to revolutionize power electronics and radio-frequency electronics in the future. However, turning SCD into useful semiconductors requires overcoming doping challenges, as conventional substitutional doping techniques, such as thermal diffusion and ion implantation, are not easily applicable to SCD. Here we report a simple and easily accessible doping strategy demonstrating that electrically activated, substitutional doping in SCD without inducing graphitization transition or lattice damage can be readily realized with thermal diffusion at relatively low temperatures by using heavily doped Si nanomembranes as a unique dopant carrying medium. Atomistic simulations elucidate a vacancy exchange boron doping mechanism that occur at the bonded interface between Si and diamond. We further demonstrate selectively doped high voltage diodes and half-wave rectifier circuits using such doped SCD. Our new doping strategy has established a reachable path toward using SCDs for future high voltage power conversion systems and for other novel diamond based electronic devices. The novel doping mechanism may find its critical use in other wide bandgap semiconductors.

cond-mat.mtrl-sci↗

arXiv2015

Thermal Diffusion Doping of Single Crystal Diamond

With the best overall electronic and thermal properties, single-crystal diamond (SCD) is the extreme wide bandgap material that is expected to revolutionize power electronics and radio-frequency electronics in the future. However, turning SCD into useful semiconductors faces doping challenges, as conventional substitutional doping techniques, such as thermal diffusion and ion-implantation, are not easily applicable to SCD. Here we report a simple and easily accessible doping strategy demonstrating that electrically activated, substitutional boron doping in natural SCD without any phase transitions or lattice damage which can be readily realized with thermal diffusion at relatively low temperature. For the boron doping, we employ a unique dopant carrying medium: heavily doped Si nanomembranes. We further demonstrate selectively doped high-voltage diodes and half-wave rectifier circuits using such doped SCD. Our new doping strategy has established a reachable path toward using SCDs for future high-voltage power conversion systems and for other novel diamond-based electronics.

cond-mat.mes-hall↗

arXiv2014

Nanopatterning by Laser Interference Lithography: Applications to Optical Devices

A systematic review, covering fabrication of nanoscale patterns by laser interference lithography (LIL) and their applications for optical devices are provided. LIL is a patterning method with simple, quick process over a large area without using a mask. LIL is a powerful technique for the definition of large-area, nanometer-scale, periodically patterned structures. Patterns are recorded in a light-sensitive medium that responds nonlinearly to the intensity distribution associated with the interference of two or more coherent beams of light. The photoresist patterns produced with LIL are the platform for further fabrication of nanostructures and growth of functional materials which are the building blocks for devices. Demonstration of optical and photonic devices by LIL is reviewed such as directed nano photonics and surface plasmon resonance (SPR) or large area membrane reflectors and anti-reflectors. Perspective on future directions for LIL and emerging applications in other fields are presented.

cond-mat.mes-hall↗