G.J. Lian

Properties of GaN-based light-emitting diode thin film chips fabricated by laser lift-off and transferred to Cu

Conventional GaN-based light-emitting diodes (LEDs) on sapphire substrates and laser lift-off (LLO) lateral current structure GaN LED thin film chips on Cu substrates have been fabricated and their properties are compared. It is found that after the LLO process, the reverse bias leakage current obviously increases and equivalent parallel resistance decreases two orders accordingly. From analyses of I–V curves the fact that tunneling behavior dominates under the reverse bias is confirmed, and the LLO process aids more defects to become tunneling active whereas the similar ideality factors and equivalent series resistances of LLO-LEDs on Cu and conventional LEDs on sapphire suggest that the LLO process does not much damage the electrical characteristics at a forward bias. The analyses of L–I curves reveal that the LLO process induces more nonradiation centers. However, the LLO-LEDs show superior performance under large injection current. The LLO-LEDs have 1.8 times greater maximum output power and 2.5 times higher current operation capabilities than the conventional LEDs within 300 mA for the good thermal conductivity of Cu.

Improved initial epitaxial growth of superconducting YBa2Cu3O7 thin films on Y-ZrO2 substrates with a La1.85Sr0.15CuO4 buffer layer

Abstract Epitaxial thin films of YBa 2 Cu 3 O 7 (YBCO) have been deposited on Y–ZrO 2 (YSZ) substrates by means of the pulse laser deposition technique. It has been found that the initial epitaxy of YBCO thin films grown on YSZ can be significantly improved by using La 1.85 Sr 0.15 CuO 4 (LSCO) as a buffer layer. X-ray diffraction measurements show that the epitaxial YBCO films have single in-plane orientation with YBCO [100]∥LSCO [100] and LSCO [100]∥YSZ [110]. The real-time resistance measurements reveal that with LSCO buffer layers the initial formation of the YBCO ultra-thin films changes from the island growth to the layer-by-layer growth.

Growth of HgBa2CaCu2Ox thin films using seed-buffer layers of YBa2Cu3Oy

Abstract High quality superconducting HgBa2CaCu2Ox (Hg-1212) thin films have been fabricated on SrTiO3 (STO) substrates using YBa2Cu3Oy (YBCO) as a seed-buffer layer (SBL). X-Ray diffraction indicates that the Hg-1212 thin films have a c-axis epitaxial structure with (100)Hg-1212//(100)STO. The φ-scans and rocking curves demonstrate that the SBL results in a better orientation of the Hg-1212 films. Scanning electron microscopy (SEM) also shows that the film surfaces are more regular. The Hg-1212 thin films on YBCO SBL have a superconducting transition temperature Tc=115–124 K and a critical current density Jc>1×106 A/cm2 at 77 K in zero field.

Growth of HgBa2CaCu2Oy films with a buffer layer

Using YBa2 Cu3 O7 (YBCO) as a buffer layer high Tc superconducting HgBa2 CaCu2 Oy (Hg-1212) thin films with zero resistance temperature (Tc ) of 115-124 K and critical current density (Jc ) of 1 MA cm-2 at 77 K in zero magnetic field have been grown on (100)Y-ZrO2 substrates. The high Tc , Jc and good morphology indicate that YBCO is a good buffer for growing the Hg cuprate films. This novel buffer makes it possible to grow Hg cuprate films on many substrates, including some metallic tapes.

Interfacial and structural characteristics of CeO2 films on silicon with a nitrided interface formed by nitrogen-ion-beam bombardment

The interfacial characteristics of CeO2/Si(100) with a nitrided layer were studied. The nitrided layer was formed by a process of nitrogen ion beam bombardment to the Si(100) substrate surface. Cerium oxide dielectric films were grown by pulsed laser deposition. The surface and structural characteristics of the nitrided layer were examined by atomic force microscopy, X-ray photoelectron spectroscopy. The interfacial structural characteristics and electrical properties of CeO2/Si(100) samples with and without the nitrided layer were analyzed by high-resolution transmission electron microscopy, current–voltage and capacitance–voltage measurements. The results show that the nitrided layer formed by nitrogen ion beam bombardment is a SiNxOy layer. Such a SiNxOy layer can effectively suppress the interfacial reactions between CeO2 and Si and is helpful to form a thinner and stable interfacial layer at the CeO2/Si(100) interface. Meanwhile, the nitrided interfacial layer is also to induce the reduced leakage current of CeO2/Si.

Structural and electrical properties of CeO/sub 2//Si with nitrided interfacial layer by nitrogen ion beam bombardment

The effects of nitrided interfacial layer between CeO/sub 2/-Si on the interfacial properties are studied. The process of nitrogen ion beam bombardment (NIBB) was used to form the nitride dielectric-Si interface. The CeO/sub 2/ high-k dielectric films were grown on Si[100] substrates by pulsed laser deposition (PLD) and the capacitors with Pt/CeO/sub 2//Si structure were fabricated. The atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), capacitance-voltage (C-V), and current-voltage (I-V) methods were used to study the interfacial characteristics of the samples. The results showed that a SiN/sub x/O/sub y/ layer was formed on Si surface by the NIBB process. The nitride layer between CeO/sub 2/ and Si can suppress the further formation of interfacial layer between CeO/sub 2/ and Si, which is helpful to improve the structural and electrical characteristics of CeO/sub 2/-Si interface.

Transport properties of Pr0.5Ca0.5(Ba1−xSrx)2Cu3O7−y(x=0,0.1,0.2,0.3) epitaxial thin films

Pr 0.5 Ca 0.5 (Ba 1-x Sr x ) 2 Cu 3 O 7-y (PCBSCO)(x=0, 0.1, 0.2, 0.3) epitaxial thin films have been prepared by the pulsed laser deposition method. By 10% Sr substitution for Ba, the T C (R=0) of the PCBSCO films increases from 35K(x=0) to 39K(x=0.1). The resistance measurments show that PCBSCO (x=0.1) films have lower resistivity (p) compared with that of PCBSCO (x=0) films. Increasing the substitution concentration x further to 0.2 and 0.3, the resistivities of the films begin to increase and the superconductivity is gradually suppressed. The effects of the oxygen content on the superconductivity of PCBSCO have also been studied.