ABSTRACT It is very common that the driven voltage of the Light emitting diode device is around 1.8eV~2.2eV, however, in its applications the voltage that applied on the circuit is higher than this specification (3 eV as usual). It will be very annoying that the design of the LED circuit should always be in series with an extra resistor in order to protect the LED. In here we propose a method with a schottky contact structure on the device that we can solve this problem. Before we proceed this method, we had better fully understand the characteristics of the material physical properties , schottky contact and ohmic contact ,also include of the process of device. The substrate of the LED diode was chosen with N-GaP(111). The metal for the ohmic contact in this device is composed of Au/Au-Ge alloy. As to the schottky contact , the metal is formed by using Au element. The techniques for characterizing these contact properties include current-voltage (I-V), specific contact resistance (rc), ideal factor and current transport etc. The LED diode is also annealed at 450ºC for 10 minutes for improving the performance. The X-ray diffraction technique is applied to Investigate the interface of the contact area. The results of this experiment are summarized below: (I) The I-V curve of Ohmic contact is linear and contact resistance irc =7

Abstract The theme of this thesis is the MBE growth of doped arsenide compound semiconductor layers including uniformly doped layers and a modulation-doped heterostructure. The Hall measurement system has been set up to measure the carrier concentration and mobility of these samples. We have also studied the ohmic contacts on epitaxial InGaAs layers by TLM method. For uniformly doped samples, the experimental relation between doping concentration and MBE cell temperature have been established, and are in good agreement with reported results. In the experiment on GaAs/AlGaAs modulation-doped heterostructure, an electron mobility of 27000[cm2/(V•s)] was obtained by cooling the sample down to 170K with liquid nitrogen. This result is consistent with published results. For P-type ohmic contacts on InGaAs, a comparison between two metal layer compositions of Cr+Zn+Au and Cr+Zn+Cr+Au was made. The Cr+Zn+Cr+Au layer gave a lowest specific contact resistance of 3.38¡Ñ10-6(ohm•cm2) at an annealing temperature of 360¢J. A N-type ohmic contact of Au+Ge+Au was also investigated. This metal layer has a lowest specific contact resistance of 9.75¡Ñ10-7(ohm•cm2) without annealing.

Thesis, (Ph. D.)--Oregon Graduate Institute, 2000.

No description available.

published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

No description available.

Dissertation (Ph.D.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Includes bibliographic references (p.55-59).

III-V semiconductor nanowires (NWs) are often referred to as one-dimensional (1-D) materials because of their high aspect ratios and excellent quantum confinement properties. Spacing between NWs in a NW array is on the order of ~102 nm, which is close to the wavelength of visible light. These properties make NWs have excellent light trapping effects and suitability for optoelectronic applications, such as solar cells and photodetectors. Gallium arsenide (GaAs) has high electron mobility and a band gap of 1.424 eV, which makes it an ideal material for solar cells. Since GaAs NWs can be grown on either GaAs substrates or foreign substrates such as silicon (Si) substrates without lattice mismatch issues, they are being widely studied for photovoltaic applications. GaAs NWs could be achieved by the vapor-liquid-solid (VLS) method in molecular beam epitaxy (MBE), or etching a GaAs substrate by inductively coupled plasma reactive ion etching (ICP-RIE). Cyclotene was used as the filling material in gaps between NWs to support a low sheet resistance front contact and prevent shunts. An In/ITO contact was developed to achieve a lower contact resistance to n-GaAs NWs than an ITO contact, while it had a similar transmittance as ITO. A crack test also showed that insertion of a thin indium layer between ITO and GaAs NWs solved the ITO crack issue during heating that resulted from a large difference in coefficients of thermal expansion (CTE) between ITO and cyclotene. Energy dispersive x-ray spectrometry (EDS) was used to determine indium diffusion into NWs, and it showed that indium diffusion was not so significant to damage the features in NWs. A novel method to achieve substrate-free NW arrays by combining ICP-RIE and selective chemical etching together was also introduced. This method made it possible to measure the transmittance of NW arrays and contact layers for the first time. Absorption of GaAs NW arrays with various NW diameters and periods were also determined experimentally. / Thesis / Master of Applied Science (MASc)

No description available.