Investigation of Mn incorporation in fifteen-period InGaAs/GaAs quantum well system

윤임택,이세준,손윤,권영해,박창수,이철진,강태원 한국물리학회 2014 Current Applied Physics Vol.14 No.8

A ferromagnetic ordering with a Curie temperature of 50 K of fifteen layer of InGaMnAs/GaAs multi quantum wells (MQWs) structure grown on high resistivity (100) p-type GaAs substrates by molecular beam epitaxy (MBE) was found. It is likely that the ferromagnetic exchange coupling of sample with Curie temperature of 50 K is hole-mediated resulting in Mn substituting In or Ga sites. Temperature and excitation power dependent PL emission spectra of InGaMnAs MQWs sample grown at temperature of 170 C show that an activation energy of Mn ion on the first quantum confinement level in InGaAs quantum well is 36 meV and impurity Mn is partly ionized. It is found that the activation energy of 36 meV of Mn ion in the QW is lower than the activation energy of 110 meV for a substitutional Mn impurity in GaAs. These measurements provide strong evidence that an impurity band existing in the bandgap due to substitutional Mn ions and it is the location of the Fermi level within the impurity band that determines Curie temperature.

Ferromagnetic Properties of Mn/Graphene/SiO2 Sheets

윤임택,손윤,권영해,강태원,박창우 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.5

In the present study, Mn/graphene/SiO2 films have been successfully prepared by spin coatinga manganese dinitrate hydrate standard solution (10,000 μg/mL Mn+2 in 2% HNO3) on agraphene/SiO2 sheet. The samples were characterized by using an X-ray diffractometer, a scanningelectron microscope, a superconducting quantum interference device and an atomic force microscope. The magnetic measurement revealed that the Mn/graphene/SiO2 films exhibited a ferromagneticbehavior at 5 K and 300 K. We concluded that the ferromagnetism observed in theMn/graphene/SiO2 sheets was associated with parasitic ferromagnetic Mn clusters imposed on theantiferromagnetic structure of MnO2, which might have resulted from a distortion of the latticestructure due to oxygen vacancies, which might have been due to the effects of magnetic and structuraldisorder introduced by a random incorporation and inhomogeneous distribution of Mn atomsin the graphene layer.

Systematic and Consistent Ferromagnetism in InMnP:Zn Bilayers for Various Mn Concentrations and Annealing Temperatures

손윤,윤임택,이세준,Y. H. Kwon,윤종승,박창수,이철진,이동진,H. S. Kim,강태원 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.11

The p-type InP:Zn epilayers were prepared by using metal-organic chemical vapor deposition,and Mn was subsequently deposited onto the epilayer by using molecular beam epitaxy. The p-typeInMnP:Zn epilayers were annealed at relatively low temperatures of 200 - 350 C and contained nosecondary phases such as InMn, MnP, and MnO2, as verified by x-ray diffraction. However, minutepresence of MnO2 was confirmed using transmission electron microscopy, which agreed with themagnetic properties measured by using a superconducting quantum interference device (SQUID). From the SQUID measurements, consistent and systematic ferromagnetic properties with clearferromagnetic hysteresis loops were observed. The Curie temperature, TC, which persisted up to 180 K, was recorded depending on the Mn concentrations and annealing temperature. Theseresults indicate that the ferromagnetic semiconductor InMnP:Zn can be fabricated at a very lowannealing temperature without forming ferromagnetic precipitates except for MnO2.

Micro- and Time-resolved Photoluminescence in GaN Nanorods with Different Diameters

박영신,윤임택,이선균,조용훈,Robert A. Taylor,임현식 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.4

We have investigated the optical properties of GaN nanorods with different diameters by using micro- and time-resolved photoluminescence measurements. Donor-bound and free exciton peaks are observed in GaN nanorods with diameters larger than 100 nm. While the relative magnitude of the free exciton emission gradually increases with decreasing nanorod diameter, there is a relative decrease in the emission from the donor bound exciton. Using time-resolved photoluminescence, the diameter dependence of the decay times for these exciton peaks is measured to be a few tens of ps. With decreasing diameter, the decay time decreases due to surface recombination.

Structural, Optical, and Magnetic Properties Related to p-type InMnP:Zn Epilayers with Curie Temperatures of Tc1 ~ 50 K and Tc2 ~ 291 K

손윤,윤임택,이세준,H. C. Jeon,Y. H. Kwon,T. W. Kang,박창수,H. S. Kim,임권택,최병춘,정중현,송태권 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.8

p-type InP:Zn epilayers were grown by metalorganic chemical vapor deposition. After the growth of InP:Zn epilayers, Mn was evaporated on top of InP:Zn epilayers using molecular beam epitaxy system. And then, Mn was diffused into InP:Zn epilayers by annealing. InMnP:Zn epilayers annealed at 600 ℃ for 60 s with the Mn concentration of both ~1.5 and ~3.0%. The optical transitions related to Mn appeared at 1.144, 1.187, 1.212 eV and 1.143, 1.179, 1.205 eV for InMnP:Zn epilayers annealed at 600 ℃ for 60 s with Mn concentration ~1.5 and ~3.0%, respectively. Transitions related to Mn are noticeably activated due to the increase of Mn concentration near 3.0 % in comparison with transitions with the Mn concentration near 1.5%. Clear ferromagnetic hysteresis loops were obtained for InMnP:Zn epilayers. Ferromagnetic hysteresis loop of InMnP:Zn epilayers annealed with the Mn concentration near 3.0% was bigger than that 1.5 % and these results agree with PL results that transitions related to Mn are remarkably activated at the annealing temperature with the Mn concentration near 3.0% in comparison with that 1.5 %. Ferromagnetic behavior persisted up Tc<SUB>1</SUB> ~ 50 K and Tc<SUB>2</SUB> ~ 291 K. Tc<SUB>2</SUB> ~ 291 K corresponds to MnP. Tc<SUB>1</SUB> ~ 50 K is originated from intrinsic InMnP:Zn, which is caused by carrier-mediated ferromagnetism in InMnP:Zn epilayer. It is found that a ferromagnetic semiconductor at Tc<SUB>1</SUB> ~ 50 K can be formed in diluted magnetic semiconductor based on InMnP:Zn epilayers additionally co-doped with Zn.

Formation of the Ferromagnetic Semiconductor InMnP:Zn through Low-temperature Annealing by Using Mn/InP:Zn Bilayer

손윤,이세준,윤임택,강태원,이영민,김득영,윤종승,박창수 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.7

The ferromagnetic semiconductor <I>p</I>-type InMnP:Zn epilayers were prepared by low temperature annealing at 250 ℃ using Mn/InP:Zn bilayers. The <I>p</I>-type InP:Zn epilayers were prepared by metal-organic chemical vapor deposition. Then, the ultra thin Mn layer was subsequently deposited onto the layers using molecular beam epitaxy. The Mn/InP:Zn bilayers were annealed at low temperature of 250 ℃ in order to minimize the formation of precipitates such as InMn, MnP, Mn<SUB>2</SUB>P, and Mn<SUB>3</SUB>In. No ferromagnetic precipitates were observed in the annealed sample InMnP:Zn; however, the sample exhibited an antiferromagnetic phase of MnO<SUB>2</SUB> that might be formed because of an unavoidable surface oxide created during the sample transfer. Despite the existence of antiferromagnetic MnO<SUB>2</SUB>, the samples revealed clear ferromagnetic hysteresis loops and showed high ferromagnetic transition temperature up to ~180 K. The results suggest that the ferromagnetic semiconductor InMnP:Zn can be effectively formed through low temperature annealing using a Mn/InP:Zn bilayer.

Multiferroic characteristics of the strained epitaxial Bi0.9Ho0.1FeO3 thin film

C. S. Park,손윤,윤임택,손종역 한국물리학회 2013 Current Applied Physics Vol.13 No.2

We fabricated high quality epitaxial Bi0.9Ho0.1FeO3 thin films which exhibited the tetragonally stained structure with a c/a ratio of about 1.04. The Bi0.9Ho0.1FeO3 thin film showed a good ferroelectric property with the high remanent polarization (Pr) of about 80 mC/cm2. The ferromagnetic hysteresis loop with a clear remanent magnetization was shown. The coercive field and the remanent magnetization of the Bi0.9Ho0.1FeO3 film are 6200 Oe and 1.7 emu/g, respectively. The abrupt conduction due to space charge limited (SCL) was revealed in leakage current density versus electric field.

복잡한 ULSI 배선 구조 생성을 위한 토포그래피 모델링 및 시뮬레이션

權五燮,원태영,尹錫仁,金演泰,尹林澤 대한전자공학회 2002 電子工學會論文誌-SD (Semiconductor and devices) Vol.39 No.4

A dynamically-allocated topographical model, so-called cell advancing model, has been developed modifying the cell model. Memory requirements are reduced by dynamically allocating completed topography and material information only at surface cells, and setting other cells as a material index. In this paper, this model is presented and verified with applications to etching process by using the analytic model and Monte Carlo model for the incident ion flux, deposition process, and process integration. In case of DRAM cell fabrication process with 5,440,500(130×155×270) cells takes about 22MB memory to represent the topography. 본 논문에서는 반도체 공정 중, 토포그래피 시뮬레이션을 수행함에 있어서, 기존의 셀 모델을 수정하여, 소요되는 메모리의 양을 최소화하는 셀 전진 모델을 개발하였다. 셀 전진 모델은, 전체 시뮬레이션 영역은 물질 정보만으로 나타내지며, 표면의 셀들만으로 리스트가 구성되고, 리스트에 표면 진화 계산에 필요한 정보가 저장된다. 개발된 시뮬레이터는 해석적 모델과 몬테카를로 모델을 이용하여 식각 공정에 있어서 입사 이온 분포가 계산되며, 단위 공정뿐만아니라 공정 순서도에 따라 적층 캐패시터 또는 디램 셀(DRAM cell) 제조 공정과 같은 통합 공정을 수행한다. 개발된 시뮬레이터를 이용하여 디램 셀 제조 공정 시뮬레이션을 수행하였을 경우에, 소요된 셀은 5,440,500(130×155×270)개였고, 메모리 양은 22MB에 불과하였다.

Enhanced ferromagnetism by preventing antiferromagnetic MnO2 in InP:Be/Mn/InP:Be triple layers fabricated using molecular beam epitaxy

이동진,박창수,이철진,송진동,구현철,윤종승,윤임택,김형상,강태원,손윤 한국물리학회 2014 Current Applied Physics Vol.14 No.4

The p-type InP:Be/Mn/InMnP:Be triple epilayers were prepared using MBE to increase Tc (>300 K) by preventing MnO2. After milling 1e3 nm of epilayers thickness from the top surface, the transmission electron microscopy (TEM) and X-ray diffraction (XRD) revealed no MnO2 and precipitates, and TEM and XRD results coincide with results of ferromagnetism. The enhanced ferromagnetic transition at >300 K corresponds to InMnP:Be. The increased ferromagnetic coupling without MnO2 is considered to originate from the increased ped hybridation. These results demonstrate that InP-based ferromagnetic semiconductor layers having enhanced ferromagnetism can be formed by above process.

Dependence of the Magnetic Properties on the Cr Content in ZnCrO Thin Films

안남현,김창민,이병호,이영민,Sanjeev K. Sharma,김득영,이세준,윤임택,손윤 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.10

We investigated the effect of the Cr content on the magnetic properties of ZnCrO thin films (Cr: 1.0 − 12.5 at.%). Regardless of the Cr concentration, all of the films exhibited clear ferromagnetism even at temperatures above 350 K. For the dependence of spontaneous magnetization on the Cr concentration, however, the magnitude of effective magnetic moment (per Cr ion) was observed to exponentially decrease with increasing Cr content. We attributed the decreased spontaneous magnetization to the degraded crystal magnetic anisotropy. Namely, we found that, in a magnetic-ion-doped thin film, the high concentration of magnetic ions caused a lattice distortion and consequently degraded the ferromagnetic channeling in the solid-state material system.