• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.9 no.1
• /
• pp.107-112
• /
• 1999

The ZnSe/GaAs epilayers were grown by RF reactive sputtering. In order to obtain the optimum condition of the growth, we have studied the dependence of Ar pressure, input power of sputter, temperature of substrate, and the distande between substrate and target. Through the observation of the grown epilayer via electronic microscope, we confirmed that the layer's surface was uniform and the boundary of the substrate and the layer was well defined. The defotmation of lattice distortion and the distortion ratio were obtained by DCRC measurements. From mrasurements of photoluminescence, in the ZnSe/GaAs sample without injection of $N_2$gas, we found that the intensity of bound exciton $I_2$is stronger than that of $I_1$and the bound exiton $I_1$represents the deep acceptor level, $I_1\;^d$. On the other hand, in the ZnSe/GaAs sample with injection of$N_2$gas, the peak of$I_1$ was much higher than that of the $I_2$and the half width appeared to be narrow. We concluded that the p-type of ZnSe/GaAs epilayer was grown successfully, because of stronger peak of the bound exciton $I_1$due to the $N_2$dopping.

• Applied Science and Convergence Technology
• /
• v.24 no.5
• /
• pp.156-161
• /
• 2015

Application of magnetic fields is important to characterize the carrier dynamics in semiconductor quantum structures. We performed photoluminescence (PL) measurements from an InGaP-AlInGaP single quantum well under pulsed magnetic fields to 50 T. The zero field interband PL transition energy matches well with the self-consistent Poisson-$Schr{\ddot{o}}dinger$ equation. We attempted to analyze the dimensionality of the quantum well by using the diamagnetic shift of the magnetoexciton. The real quantum well has finite thickness that causes the quasi-two-dimensional behavior of the exciton diamagnetic shift. The PL intensity diminishes with increasing magnetic field because of the exciton motion in the presence of magnetic field.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.229.1-229.1
• /
• 2016

본 연구에서는 Hole Transporting Layer(HTL)와 Electron Transporting Layer(ETL)의 두께에 의한 특성을 비교해보기 위해서 각각 0, 10, 20 nm로 HTL, ETL 두께를 달리한 형광 OLED소자를 제작하였다. ETL의 두께가 얇아질수록 $V_{TH}$ 값은 2.5V에서 0.9 V로 낮게 나타났고 소자의 전체 두께와 on voltage는 비례한다는 특성을 발견할 수 있었다. HTL과 ETL이 두꺼울수록 각 layer에서 carrier들의 이동에 delay가 생기고 emission layer에서 표면까지 거리가 생기기 때문이다. ETL의 두께가 두꺼울수록 높은 luminance 값을 나타내는 차이를 보여주고 있다. Hole에 비해 이동도가 작은 electron은 emission layer까지 늦게 전달되어, EML내에서 비교적 cathode쪽에 가까운 곳에서 exciton이 형성되기 때문이다. CE에도 더 두꺼운 ETL을 가진 소자가 더 높은 CE값 가짐을 확인할 수 있다. 모든 소자가 $200mA/cm^2$에서 가장 높은 CE값을 나타낸 이유는 $200mA/cm^2$에서 electron-hole 결합이 만들어내는 exciton형성이 가장 많기 때문이다. PE, QE도 ETL 두께가 두꺼울수록 특성을 향상이다. 결론적으로 ETL의 두꺼울수록 current density값이 감소함을 보이고 있는 반면 turn on voltage, luminance, efficiency 증가함을 볼 수 있다.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2005.07b
• /
• pp.1381-1382
• /
• 2005

We report improved efficiency in blue electrophosphorescent organic light emitting diodes by introducing an interfacial exciton blocking layer between light emitting layer (EML) and hole transport layer (HTL). Iridium(III) bis [(4,6-di-fluorophenyl)- pyridinato -N,C2']picolinate (FIrpic) was used as blue phosphorescent dopant and JHK6-3 with carbazole and electron transporting group as host and also as the interfacial layer, resulting in drastic increase in quantum efficiency.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2010.06a
• /
• pp.378-378
• /
• 2010

The ZnSe epilayers were grown on the GaAs substrate by hot wall epitaxy. After the ZnSe epilayers treated in the vacuum-, Zn-, and Se-atmosphere, respectively, the defects of the epilayer were investigated by means of the low, temperature photoluminescence measurement. The dominant peaks at 2.7988 eV and 2.7937 eV obtained from the PL spectrum of the as-grown ZnSe epilayer were found to be consistent with the upper and the lower polariton peak of the exciton, $I_2$ ($D^{\circ}$, X), bounded to the neutral donor associated with the Se-vacancy. This donor-impurity binding energy was calculated to be 25.3 meV. The exciton peak, $I_l^d$, at 2.7812 eV was confirmed to be bound to the neutral acceptor corresponded with the Zn-vacancy.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2010.06a
• /
• pp.380-380
• /
• 2010

The chalcopyrite $ZnIn_2S_4$ epilayers were grown on the GaAs substrate by using a hot-wall epitaxy (HWE) method. The crystal field and the spin-orbit splitting energies for the valence band of the $ZnIn_2S_4$ have been estimated to be 0.1541 eV and 0.0129 eV, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the ${\Delta}so$ definitely exists in the $\Gamma_5$ states of the valence band of the $ZnIn_2S_4$/GaAs epilayer. The three photocurrent peaks observed at 10 K are ascribed to the $A_{1^-}$, $B_{1^-}$, and $C_1$-exciton peaks for n = 1. Also, we obtained the $A_{\infty^-}$ and B-exciton peaks from the PC spectrum at 293 K.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.30 no.2
• /
• pp.126-132
• /
• 2017

The power conversion efficiency of organic polymer solar cells was enhanced by introducing a ferroelectric polymer layer at the interface between active layer and metal electrode. The power conversion efficiency was increased by 50% through the enhancement of the open circuit voltage. To investigate the role of the ferroelectric layer on the dissociation process of the excitons, non-radiative portion of the exciton decay was directly measured by using photoacoustic technique. The results show that the ferroelectric nature of the buffer layer does not play any roles on the dissociation process of the excitons, which indicates the efficiency enhancement is not due to the ferroelectricity of the buffer layer.

• Transactions on Electrical and Electronic Materials
• /
• v.8 no.5
• /
• pp.191-195
• /
• 2007

We investigated photoluminescence characteristics of ZnO nano needle-like rods grown on a c-plane $AL_2O_3$ substrate by the hot wall epitaxy method. The nano-rods were vertically well aligned along the ZnO c-axis. The diameters of the ZnO nano-rods ranged from 20 nm to 30 nm and their lengths were between 600 and 700 nm. In the photoluminescence spectrum at 10 K, the exciton emission bound to the neutral donor dominated while defect related emission was weakly observed. With a further increase of temperature, the free exciton emission appeared and eventually became dominant at room temperature.

• Ceramist
• /
• v.21 no.2
• /
• pp.19-28
• /
• 2018

Coulomb drag is an effective probe into interlayer interaction between two electron systems in close proximity. For example, it can be a measure of momentum, phonon, or energy transfer between the two systems. The most exotic phenomenon would be when bosonic indirect excitons (electron-hole pairs) are formed in double layer systems where electrons and holes are populated in the opposite layers. In this review, we present various drag phenomena observed in different double layer electron systems, e.g. GaAs/AlGaAs heterostructures and two-dimensional material based heterostructures. In particular, we address the different behavior of Coulomb drag depending on its origin such as momentum or energy transfer between the two layers and exciton condensation. We also discuss why it is difficult to achieve electron-hole pairs in double layer electron systems in equilibrium.

• Journal of Electrical Engineering and information Science
• /
• v.2 no.6
• /
• pp.106-110
• /
• 1997

The binding energies of the ground state of both the heavy-hole and light-hole excitons in a GaAs(In\ulcornerGa\ulcornerAs) quantum well sandwiched between two semi-infinite Al\ulcornerGa\ulcornerAs(InP) layers are calculated as a function of well width in the presence of an arbitray magnetic field. A variational approach is followed using very simple trial wave function. The applied magnetic field is assumed to be parallel to the axis of growth and the binding energies are calculated for a finite value of the height of the potential barrier. The exciton binding energies for a given value of the magnetic field are found to be increased than their values in a zero magnetic field due to the compression of their wave functions within the well with the applied magnetic field.