Jin Soak Kim

Origin of clear ferromagnetism for p-type GaN implanted with Fe+ (5 and 10at.%)

The systematic enhancement of ferromagnetic hysteresis loops for GaN implanted with high doses of Fe (5→10at.%) takes place with an increase in the annealing temperature from 700to850°C. The trends of magnetic properties coincide with the results of the increased full width at half maximum of triple axis diffraction for GaN (0002), including the appearance of GaFeN, the enhanced Fe-related photoluminescence transitions, and the systematic increase in sizes of symmetric spin ferromagnetic domains GaFeN in atomic force microscopy and magnetic force microscopy.

Zero-internal fields in nonpolar InGaN/GaN multi-quantum wells grown by the multi-buffer layer technique

The potential of nonpolar a-plane InGaN/GaN multi-quantum wells (MQWs), which are free from a strong piezoelectric field, was demonstrated. An a-GaN template grown on an r-plane sapphire substrate by the multi-buffer layer technique showed high structural quality with an omega full width at half maximum value along the c-axis of 418 arcsec obtained from high-resolution x-ray diffraction analysis. From barrier analysis by deep level transient spectroscopy, it appeared that a-plane InGaN/GaN MQWs can solve the efficiency droop problem as they have a lower electron capture barrier than the c-plane sample. The peak shift of the temperature-dependent photoluminescence signal for the nonpolar InGaN/GaN MQWs was well fitted by Varshnis empirical equation with zero-internal fields. A high photoluminescence efficiency of 0.27 from this sample also showed that nonpolar MQWs can be the key factor to solve the efficiency limitation in conventional c-plane GaN based light emitting diodes.

Study on Defect States in GaN Epilayer Induced by Irradiation of High-Energy Electrons

The defect states of an electron-beam irradiated GaN epilayer were characterized by capacitance–voltage (C–V) and deep-level transient spectroscopy (DLTS) measurements. The electron irradiation was performed using 1 and 2 MeV energy beams with 1 ×1015 and 1 ×1016 cm-2 doses, respectively. The depth penetrated in the GaN epilayer by 1 MeV electrons appeared to be about 450 to 600 nm from the C–V measurement. Five defect states with activation energies of 0.34, 0.49, and 0.65 eV including two broad signals were observed by DLTS measurements, and it was suggested that they might originate from crystal damage during high-energy electron irradiation.

Field dependence of barrier heights and luminescence properties in polar and nonpolar InGaN/GaN single quantum wells

The external field dependence of barrier heights and the internal field dependence of luminescence properties in InxGa1−xN/GaN single quantum wells (SQWs) with polar (x=0.13) and nonpolar (x=0.15) orientations were investigated. The conduction band offset of a SQW was characterized by using deep level transient spectroscopy. At a reverse bias of −3 V, the barrier height of the nonpolar SQW was estimated to be 0.42 eV, which is smaller than the 0.60 eV seen in the polar SQW due to the absence of internal fields along the nonpolar direction. Both samples showed a redshift of barrier heights with increasing reverse bias. The carrier recombination affected by carrier localization, quantum-confined Stark effect, and Varshni’s shift was analyzed through temperature-dependent photoluminescence. Numerical simulations of the barrier heights and internal fields showed good agreement with experimental results.

Electrical characterization of GaAs/AlGaAs multi-quantum wells for quantum cascade laser

In this study, we investigated the electrical properties of three QW active region by capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS) measurements (Blood, 1992 and Kim, 2004). Then, the optical properties were measured also by photoluminescence (PL) and Fourier transformed infra-red spectroscopy (FTIR), etc. In this study, we prepared GaAs/AlGaAs single and three QWs samples grown on n-GaAs substrates as a simplified active region except for other complex regions of QCL device. Generally, the QCL structure has made up of 26th/spl sim/40th period of the injection/active region, but the structure is too complicated to analyze electrical properties. Thus, we used simple structure in this study. And then, in order to measure C-V and DLTS, a Schottky diode was made by Au-gate formation and indium ohmic contact below the backside.

Carrier Dynamics of Deep-Level States in InGaN/GaN Multiquantum Wells

InGaN/GaN (3 nm/10 nm) multiquantum wells (MQWs) were grown on (0001) sapphire substrates by metal–organic chemical vapor deposition. To characterize the effect of internal electric fields on deep-level states in InGaN MQWs, deep-level transient spectroscopy (DLTS) and bias-dependent photoluminescence (PL) measurements were performed. The thermal activation energy of MQWs obtained from DLTS spectra decreased to 0.15 eV with an increase in reverse measure bias from 2 to 10 V, which indicates partially cancelled internal fields. The blue shift of PL peak energy was about 0.05 eV when the reverse measure bias was changed from 0 to 5 V. This is explained well by carrier dynamics in the conduction band of InGaN/GaN MQWs, which affects carrier recombination energies corresponding to the band edge to edge transitions with changing reverse measure bias. # 2009 The Japan Society of Applied Physics

Electrical properties of InAs/InGaAs/GaAs quantum-dot infrared photodetectors

In this study, electrical properties of the InAs/GaAs quantum-dot infrared photodiodes (QDIP) were characterized by performing capacitance-voltage (C-V) and DLTS measurements.

Structural, electrical, and optical characterizations of a-plane InGaN/GaN quantum well structures

Sung-Ho Lee, Jae Bum Kim, Ji-Su Son, and Sung-Min Hwang Green Energy Research Center, Korea Electronics Technology Institute, Gyeonggi-do 463–816, Korea GaN and related ternary compounds have been widely used for fabrication of light emitting diodes (LEDs) and laser diodes (LDs). Especially, the low-dimensional systems such as quantum wells (QWs), quantum wires, and quantum dots have been investigated as an effective structure for improving the efficiency of light-emitting devices such as light emitting diodes and laser diodes. Generally, the quantum well active regions in III-nitride optoelectronic devices grown on conventional templates along the polar orientation have critical problems given by the quantum confined Stark effect (QCSE) due to the effects of strong piezoelectric and spontaneous polarizations [1]. However, the QWs grown on nonpolar templates along a- or m-directions are free from the QCSE since the polar-axis lies within the growth plane of the template [2]. In this study, we achieved high quality a-plane GaN films on sapphire substrates and characterized structural, electrical and optical properties in the a-plane InGaN/GaN QW structures. High quality of a-plane GaN templates was confirmed by using selected area diffraction (SAD) patterns and high resolution x-ray diffraction (HRXRD) results. To investigate the electrical properties of aplane GaN QWs structures, the temperature-dependent carrier depth profiles which can determine the carrier confinement with nanoscale spatial resolution were studied. And the redshift of photoluminescence (PL) peaks with increasing temperature will be intensively discussed.

Relevant correlation between electrical and magnetic properties for p-type InP:Zn implanted with Mn (10 at. %)

A relevant correlation between magnetic properties and Mn-related deep level states for the Mn-implanted p-type InMnP:Zn layers annealed at 400–600 °C was investigated. For the 600 °C-annealed sample, the portion of deep level transient spectroscopy signals corresponding to Mn-related states was observed to significantly increase while that related to charge-trapping centers observed for 400 and 500 °C-annealed samples drastically decreased. The sample showed the improved ferromagnetic properties compared with other samples. These results are considered as originating from the effective incorporation of Mn ions into the InP:Zn host lattice with recovering the crystallinity after thermal annealing.

A study on the energy bands of multi-quantum wells in the quantum cascade laser structure by deep-level transient spectroscopy

We have investigated the defect states and confined energy levels of three quantum wells (QWs) in the quantum cascade laser (QCL) structure by capacitance–voltage and deep-level transient spectroscopy methods. Defect states with activation energies in the range of 0.49–0.88 eV were obtained in the GaAs capping layer, and their origins were considered as EL3 and EL2 families, which are well-known deep levels of GaAs materials. The densities of these defects in the GaAs capping layer of the QCL structure were about 3–12% of the donor concentration. The confined energy levels of QWs showed activation energies of about 130 meV and 230 meV from the top of the AlGaAs barrier, and their carrier confinement ability was measured to be about 0.5% of the donor concentration.