• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.33-38
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• 2000

The ~1540 nm Er$^{3+}$ photoluminescence (PL) and photoluminescence excitation (PLE) spectra of Er-implanted Mg-codoped GaN (GaN:Er+Mg) exhibit that the excitation efficiency of a specific Er$^{3+}$ center among different Er$^{3+}$ centers existing in Er-implanted GaN is selectively enhanced, compared to Er-implanted undoped GaN (GaN:Er). In GaN:Er+Mg, the 1540 nm PL peaks characteristic of the so-called "violet-pumped" Er$^{3+}$ center and the ~2.8-3.4 eV (violet) PLE band are significantly strengthened by the Mg-doping. The intra-f absorption PLE bands associated with this "violet-pumped" center are also enhanced by this doping. The 1540 nm PL peaks originating from the violet-pumped center dominate the above-gap-excited Er$^{3+}$ PL spectrum of GaN:Er+Mg, whereas it was unobservable under above-gap excitation in GaN:Er. All of these results indicate that Mg doping increases the efficiency of trap-mediated excitation of Er$^{3+}$ emission in Er-implanted GaN.planted GaN.

• Korean Journal of Materials Research
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• v.18 no.8
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• pp.450-453
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• 2008

Mg-doped and In-Mg co-doped p-type GaN epilayers were grown in a low-pressure metal organic chemical vapor deposition technique. The effect of In doping on the p-GaN layer was studied through photoluminescence (PL), persistent photoconductivity (PPC), and transmission electron microscopy (TEM) at room temperature. For the In-doped p-GaN layer, the PL intensity increases significantly and the peak position shifts to 3.2 eV from 2.95 eV of conventional p-GaN. Additionally, In doping greatly reduces the PPC, which was very strong in conventional p-GaN. A reduction in the dislocation density is also evidenced upon In doping in p-GaN according to TEM images. The improved optical properties of the In-doped p-GaN layer are attributed to the high crystalline quality and to the active participation of incorporated Mg atoms.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.1
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• pp.1-10
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• 1995

Congruent $LiNbO_3$ single crystals and $LiNbO_3$ : Mg single crystals, having high resistance to optical damage, doped with MgO to the levels of 2.0, 5.0 and 7.0 mol% were grown successfully by CZ method and optical damage of each crystal was measured by compen. sation method. With doping level reaching about 5 mol%, there was an abrupt change in the features of optical absorption edge and $OH^-$ absorption band. From these data, we confirmed indirectly the threshold in MgO doping level. When the MgO doping amount reaches about 5 mol% in the melt, $Mg^{2+}$ occupies Nb site and becomes $Mg_{Nb}^{2+}$, resulting in the sharp increase of optical damage resistance. The optical damage resistance of $LiNbO_3$ : Mg was improved more than three times when MgO amount in the melt reaches 5 mol%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.177-180
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• 2004

발광층에 Alq3와 rubrene을 mixed host로 사용하고 DCJTB를 형광 dopant로 사용한 다층 박막 구조의 red OLEDs를 제작하였다. 소자의 구조는 $ITO:Anode(120nm)/{\alpha}-NPD:HTL(40nm)/Alq_3+Rubrene(mixed\;host\;1:1)+DCJTB(red\;dopant\;3%)+:EML(20nm)/Alq_3:ETL(40nm)/MgAg(Mg\;5%\;wt):Cathode(150nm)$ 로서 EML내부에 DCJTB를 Totally Doping Method와 Dotted-Line Doping Method의 두 가지 방법으로 도핑 하였다. Mixed host구조에 DCJTB를 6구간으로 나누어 Dotted Line Doping한 소자는 luminance yield가 $9.2cd/A@10mA/cm^2$ 이었다. 이 소자는 DCJTB만을 Totally Doping한 소자의 luminance yield $3.2cd/A@10mA/cm^2$에 비해 약 190%정도의 높은 효율 향상을 보였다. 또한 $10mA/cm^2$에 도달하는 전압은 5.5V Vs. 8.5V로서 mixed host를 사용한 소자에서 약 3V정도 구동전압이 낮아지는 효과가 있었다. 발광 스펙트럼의 Full Width Half Maximum(FWHM)은 각각 56.6nm와 61nm로서 rubrene을 mixed host로 사용한 소자에서 높은 색 순도를 얻을 수 있었다. 이러한 성능의 향상은 $Alq_3$와 혼합된 rubrene에 의한 낮은 전하주 입장벽, 높은 전류밀도에서 나타나는 발광감쇄현상의 감소, 그리고 발광층의 DLD구조에 의한 전하의 trap & confinement 에 따른 발광 exciton의 형성확률이 증가한데서 나타났다고 생각된다.

• Progress in Superconductivity
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• v.14 no.1
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• pp.34-38
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• 2012

The effect of graphene inclusion in the ex-situ $MgB_2$ was analyzed with the help of resistivity behavior and critical current density studies. Amount of graphene was systematically varied from 0% for pristine sample to 3% by the weight of $MgB_2$. Graphene that is considered as a good source of carbon was found to be intact without any significant carbon doping in $MgB_2$ structure as reveled by XRD measurements. There was no signature of graphene inclusion as far as the superconducting transition is concerned which remained same at 39 K for all the samples. The transition width being sensitive to defect doping remained more or less about 2 K for all the samples showing no variation due to doping. Although there was no change in the superconducting transition or transition width, the graphene doped sample showed noticeable decrease in the overall resistivity behavior with respect to decrease in temperature. The graphene inclusion acted as effective pinning centers which have enhanced the upper critical field of these samples.

• Journal of Magnetics
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• v.16 no.1
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• pp.15-18
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• 2011

We have studied the $TiO_2$ doping effects on the flux pinning behavior of an $MgB_2$ superconductor synthesized by the in-situ solid-state reaction. From the field-cooled and zero-field-cooled temperature dependences of magnetization, the reversible-irreversible transition of $TiO_2$-doped $MgB_2$ was determined in the H-T diagram (the temperature dependence of upper critical magnetic field and irreversibility line). For comparison, the similar measurements are also obtained from SiC-doped $MgB_2$. The critical current density was estimated from the width of hysteresis loops in the framework of Bean's model at different temperatures. The obtained results manifest that nano-scale $TiO_2$ inclusions served as effective pinning centers and lead to the enhanced upper critical field and critical current density. It was concluded that the grain boundary pinning mechanism was realized in a $TiO_2$-doped $MgB_2$ superconductor.

• Progress in Superconductivity
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• v.10 no.1
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• pp.17-22
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• 2008

We have examined the effect of ball-milling on the superconducting properties of $MgB_2$ doped with C. The ball-milling of pre-reacted $MgB_2$ powder was carried out in dry or wet state using C or diethylenetriamine ($C_{4}H_{13}N_3$) as additives. The diethylenetriamine, whose chemical formula contains no oxygen, was chosen to avoid an excess oxidation during doping. The superconducting transition temperature (Tc) of the ball-milled or doped $MgB_2$ powders was only slightly smaller than that of undoped $MgB_2$. The critical current density (Jc) of the highly ball-milled $MgB_2$ was higher than that of C-doped $MgB_2$. The addition of diethylenetriamine was detrimental to Jc, although Tc was almost unchanged.

• Journal of Sensor Science and Technology
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• v.31 no.1
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• pp.31-35
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• 2022

The efficacy improvement of the light emitting diode (LED) was studied for the realization of small-size, low power consumption, and highly sensitive bio-sensor instrument. The performance of the LED with Mg delta-doping at the interface of AlGaN/GaN super-lattice in p type cladding layer was simulated. The device with Mg delta-doping showed improved current, radiative recombination rate, electroluminescence, and light output power compared to the conventional LED structure. Under the bias condition of 5 V, the improved device exhibited 20.8% increase in the light output power. This is attributed to the increment of hole concentration from stable ionization of Mg in p type cladding layer. This result is expected to be used for the miniaturization, power saving, and sensitivity improvement of the bio-sensor system.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.6
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• pp.235-242
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• 2018

High temperature electrical conductivity of Aluminum Nitride (AlN) ceramics sintered with $Y_2O_3$ as a sintering aid has been investigated with respect to various sintering conditions and MgO-dopant. When magnesium oxide is added as a dopant, liquid glass-film and crystalline phases such as spinel, perovskite are formed as second phases, which affects their electrical properties. According to high temperature impedance analysis, MgO doping leads to reduction of activation energy and electrical resistivity due to AlN grains. On the other hand, the activation energy and electrical resistivity due to grain boundary were increased by MgO doping. This is a result of the formation of liquid glass film in the grain boundary, which contains Mg ions, or the elevation of schottky barrier due to the precipitation of Mg in the grain boundary. For the annealed sample of MgO doped AlN, the electrical resistivity and activation energy were increased further compared to MgO doped AlN, which results from diffusion of Mg in the grains from grain boundary as shown in the microstructure.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.06a
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• pp.139-143
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• 1997

The doping effects of Mg and/or Fe ions on congruent LiNbO$_3$ single crystal growth were studied in order to clarify the roles of MgO in Fe doped LiNbO$_3$ single crystals. The effective distribution coefficienct of Fe was found decreased drastically from 0.85 to 0.5 by the addition of MgO into the LiNbO$_3$ melt. M ssbauer spectra revealed that the addition of MgO reduces the occurrence of Fe2+ ions during growth in air. Therefore, it is likely that there would be two important roles of MgO in Fe doped LiNbO$_3$. One is to suppress the incorporation of all Fe ions, and the other is to reduce the concentration of Fe2+ ions among the total Fe ions.