S.-W. Lee

Clarification of Mn–Zn interaction for InMnP:Zn epilayer by photoluminescence and x-ray photoelectron spectroscopy

Transition related to the Mn–Zn interaction was observed in photoluminescence (PL) study of the InMnP:Zn epilayer and the peak position blueshifted with increasing Mn concentration. X-ray photoelectron spectroscopy was used to clarify the blueshift of the PL peak. The binding energy shifts of Mn 2p and Zn 2p core levels indicative of the interaction between Mn and Zn were observed. This mutual interaction between Mn 2p and Zn 2p agrees with the result that the Mn-related transition in InMnP:Zn codoped with Zn is shifted to the higher energy region in comparison with InMnP without additional doping of Zn.

Ferromagnetic formation of two phases due to MnP and InMn3 from InMnP:Zn implanted with Mn (10at.%)

InMnP:Zn samples implanted with Mn (10at.%) were annealed at 350°C for 60s and at 450°C for 30s. Using transmittance electron microscopy, both single crystalline and polycrystalline structures containing MnP and InMn3 sized ∼20nm were observed depending on the annealing condition. These samples exhibited two different Curie temperatures: TC1 at 291K and another well above 291K. The high temperature-ferromagnetic behavior up to TC1 and above TC2 is believed to have originated from two magnetic MnP and InMn3 phases, respectively.

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.

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.

Photoconductivity in lateral conduction self-assembled Ge/Si quantum dot infrared photodetectors

We have investigated the photocurrent spectra of lateral conduction self-assembled Ge/Si quantum dots (QDs) infrared photodetector structure. We have observed a broad mid-infrared photocurrent spectrum in photon energy range of 120-400 meV (λ~3-10 μm) due to bound-to-bound as well as bound-to-continuum intersubband transition of normal incidence radiation in the valence band of self-assembled Ge QDs and subsequent lateral transport of photoexcited carriers in the Si/SiGe two-dimensional channel. The peak responsivity was as high as 134 mA/W at photon energy of 240 meV (λ~5.2 μm) at T=10 K and Vb=8 V.