This work investigates the physical properties of the MgxZn1-xO films. MgxZn1-xO films were deposited by RF
magnetron sputtering system using a 6 inch ZnO/MgO (80/20 wt%) target. The XPS, Hall measurement, and transparent
performance are measured. The XPS results show that there is high Carbon element content on the surface of MgxZn1-xO
maybe due to the contamination and the average of the Mg content is about 25 at. %. The XRD results indicate that the
appearance of only (111) peaks for as-grown MgxZn1-xO film is a sign of the cubic single phase. In this study, the
MgxZn1-xO film show high transparency with transmittances over 90 % in the visible region (400 ~ 700nm) and the sharp
absorption edge is visible in UV region due to the Mg content. Therefore, the Hall measurement of MgxZn1-xO films
which were deposited at lower RF power show the higher doping concentration, the lower resistivity and higher mobility
as a function of the annealing temperatures. The experimental results indicate that MgxZn1-xO film with 800 °C
annealing contains more oxygen vacancies which play the role of donor. Since oxygen vacancies generate states in the
band gap and cause an increase in conductivity.
This work investigates the reactive ions etching (RIE) physical properties of n-type ZnO using H2/CH4 and H2/CH4/Ar
mixtures by varying the gas flow ratio, the radio-frequency (rf) plasma power and the chamber pressure. Atomic force
microscopy (AFM) results and surface topographies are discussed. Although the etching rate of the n-ZnO at an H2/CH4
flow rate of 100/0 sccm, a work pressure of 100 mTorr and an rf power of 300 W is lower than under any other
conditions, the rms roughness of 43.78 nm is the highest, and supports the application of roughened transparent contact
layer (TCL) in light-emitting diodes (LEDs). The dynamics associated with the high etching rate were highly efficient at
an H2/CH4/Ar flow rate of 38/5/57 sccm, a work pressure of 150 mTorr and an rf power of 300 W. In addition, the ZnO
with thermal annealing were studied. The slower etching rate of annealed n-ZnO is observed due to an increase the
crystal quality of the ZnO films after thermal annealing which consists with the x-ray diffraction (XRD) results.
In this study, ZnO:Al(AZO) Ni/AZO and NiOx/AZO films were deposited on p-type GaN films followed by thermal
annealing to form Ohmic contacts. After thermal annealing, the resistivities reduced from 5×10-3 to 4.4×10-4 Ω-cm,
2.6×10-3Ω-cm, and 1.1×10-3Ω-cm for AZO, Ni/AZO, and NiOx/AZO films, respectively. The Ohmic characteristic
could be highly improved after inserting Ni and NiOx between AZO and p-GaN. Both the Ni/AZO and NiOx/AZO
contacts exhibit Ohmic characteristic after annealed at 800°C in N2 ambient. The light transmittance of Ni/AZO and
NiOx/AZO films were higher than 80% in the range of 380-700nm after the 800°C -annealing treatment. In addition,
we fabricated InGaN/GaN MQW LEDs with a dimension of 1×1mm2 using the transparent Ni/AZO and NiOx/AZO
Ohmic contact as a current spreading layer for p-GaN in order to increase the light extrication efficiency. For the LED
with Ni/AZO contact, the light output approach to saturation when the injection current was about 400mA. But the
light output still doesn't approach to saturation when the injection current was 500mA for the LED with NiOx/AZO
contact. This may be due to that the resistivity of Ni/AZO was higher than that of NiOx/AZO and exhibit more heavy
current clouding effect. The increasing of resistivity may be due to the interdiffusion of Ni into AZO. Comparing to
GaN LED with Ni/Au ohmic contact, the light output intensity of LEDs with Ni/AZO and NiOx/AZO contacts was
increased by 41% and 60% at 350mA, respectively.
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