Jui-Tai Ku

The Roles of Threading Dislocations on Electrical Properties of AlGaN/GaN Heterostructure Grown by MBE

The role played by different types of threading dislocations (TDs) on the electrical properties of AlGaN/GaN heterostructure grown by plasma-assisted molecular beam epitaxy (MBE) was investigated. Samples with different defect structures and densities were prepared and measurements were taken from the same sample to study the correlative behavior of various TDs. From the Hall measurement, the electron mobility in two-dimensional electron gas channel was mainly controlled by the edge dislocation, which has a dominant amount in the material. The edge TDs acted as Coulomb scattering centers inside the channel and reduces the carrier mobility and increased its resistance. Screw TDs played a much significant role than edge TDs in determining the reverse-bias leakage current of Schottky barrier diodes. Leakage current is affected slightly by the reduction of free carrier density in the channel for samples with a higher edge TD density, but screw TD, which acted as the current leakage path, was more deleterious to the reverse-bias leakage current of AlGaN/GaN structure.

Time-resolved photoluminescence of isoelectronic traps in ZnSe1−xTex semiconductor alloys

Kohlrausch’s stretched exponential law correlates well with the photoluminescence (PL) decay profiles of ZnSe1−xTex. As the Te concentration increases, the stretching exponent β initially declines and then monotonically increases. This result can be understood using the hopping-transport and energy transfer model. The increase in the number of isoelectronic Te localized traps can reduce the PL decay rate and increase the linewidth, whereas the hybridization of the Te localized states with the valence-band edge states causes a reduction in both the lifetime and linewidth.

Epitaxial Overgrowth of Gallium Nitride Nano-Rods on Silicon (111) Substrates by RF-Plasma-Assisted Molecular Beam Epitaxy

Strain-free gallium nitride (GaN) overgrowth on GaN nano-rods is realized by RF-plasma assisted molecular beam epitaxy (RF-MBE) on silicon (Si) substrate. The strain-free condition was identified by the strong free A exciton (FXA) photoluminescence (PL) peak at 3.478 eV and the E2 high phonon Raman shift of 567 cm-1. It is clearly demonstrated that the critical diameter of GaN nano-rods is around 80 nm for the overgrowth of strain-free GaN. The blue-shift of PL peak energy and phonon Raman energy with decreasing the diameter of nano-rod result from the strain relaxation of overgrowth GaN.

Epitaxial overgrowth of GaN Nanorods on Si (111) substrates by rf-plasma-assisted molecular-beam Epitaxy

Department of Electrophysics, National Chiao Tung University, Hsin-Chu, Taiwan 30010, R.O.C. Department of Electronics Engineering, National Chiao Tung University, Hsin-Chu, Taiwan 30010, R.O.C. Microelectronics and Information Systems Research Center, National Chiao Tung University, HsinChu, Taiwan 30010, R.O.C. Department of Materials Science and Engineering, National Chiao Tung University, Hsin-Chu, Taiwan 30010, R.O.C. Phone: +886-3-5712121-56182, Fax: +886-3-5715506, E-mail: wuchingchou@mail.nctu.edu.tw

Dependence of GaN Defect Structure on the Growth Temperature of the AlN Buffer Layer

The defect structure of the GaN film grown on sapphire by plasma-assisted molecular beam epitaxy (PAMBE) technique was found to be dependent on the AlN buffer layer growth temperature. This buffer growth temperature controlled the defect density in GaN film but had shown contrary effects on the density of screw threading dislocation (TD) and edge TD. The density of screw TD was high on lower temperature buffer but low on the higher temperature buffer. Meanwhile the density of edge TD had shown the opposite. Further examinations have suggested that the defect structure was closely related to the stress in the GaN film, which can be controlled by the growth temperature of the AlN buffer. Using the 525°C AlN buffer, optimum quality GaN film with relatively low screw and edge TDs were achieved.

A method for suppressing deep-level emission in ZnSe/Ge/GexSi1-x/Si structure

1 Department of Electrophysics, 1001 Ta Hsueh Road, National Chiao Tung University, Hsin-chu 300, Taiwan, R.O.C. 2 Microelectronics and Information Systems Research Center, 1001 Ta Hsueh Road,National Chiao Tung University, Hsinchu 300, Taiwan, R.O.C. Phone: +886-3-5712121-52981 E-mail: kondo.mse89g@nctu.edu.tw 3 National Nano Device Laboratories, 26, Prosperity Road I, Science-based Industrial Park, Hsin-chu 300, Taiwan, R.O.C. 4 Institute of Physics, Academia Sinica, 128 Academia Rd, Nankang, Taipei, Taiwan, R.O.C.