The Studies Of Submicro/Nanometer Electrodes And Their Interfacial Contact Properties In Optoelectronic Devices

The contact properties between electrodes and semiconductors are the key factors influencing the energy efficiency, reliability and life time of optoelectronic devices. High contact resistance results in not only waste of energy, but also increase of work temperature and consequential reduction of the device reliability and life time. Lowering the contact resistance is one of the important and difficult issues in this field. Using interfacial insertion layer is a common method to improve the performance of optoelectronic devices. The interfacial insertion layer can significantly reduce the interfacial potential barrier between the electrode and semiconductor, so as to improve the charge transport efficiency. This work studies the effects and mechanism of interface insertion layer on the interface electrical properties of two kinds of optoelectronic devices, light emitting diode(LED) and organic thin film transistor(OTFT). The main results are as follows: 1. Sputter-grown Ga-doped Zn O transparent conducting layer was studied as a low cost electrode in LED. The sputtering power, deposition time, substrate temperature and argon gas flow were studied to optimize the properties of GZO thin film. The lowest resistivity of 2.79×10-4Ω?cm2 was obtained at the sputtering power 300 W, the substrate temperature 300℃ and the argon gas flow 40 sccm. Besides, the light transmittance of the film has reached 97.9% in the wavelength of 460 nm. This will lay the foundation for the following study of GZO electrodes. 2. The CuxS insertion layer was used to improve the contact properties of GZO/p-Ga N. The influence of CuxS thickness, annealing temperature and atmosphere on the performance of GZO/p-Ga N contact was studied. The CuxS/GZO composite electrodes have good transparency; all light transmittances at the wavelength of 460 nm exceed 80%. The sample annealed at 500℃ in air achieved a good ohmic contact with a specific contact resistance of 1.66×10-2Ω·cm2. The forward voltage of the LED with 5nm of CuxS layer reached 3.67 V, which is 1.78 V lower than the forward voltage of the LED without CuxS insertion layer. To reveal the formation mechanism of the ohmic contact, AES and XPS were used to analyze the composition of the GZO/CuxS/p-Ga N interfaces. The result suggests that the interface reactions and atomic diffusions are responsible for the formation of the low contact resistance. 3. p-InxGa1-xN strained layer was used as the interlayer between p-Ga N and GZO to improve the contact properties. It is found that the high energy plasma induced during sputtering can damage the p-InxGa1-xN layer resulting in poor contact properties of GZO/p-Ga N. However, by reducing the sputtering power to a very low value, ohmic contact was formed. The specific contact resistivity of the GZO/p-Ga N contact obtained at 50 W sputtering power and annealed at 650℃ in nitrogen atmosphere was calculated to be 4.07×10-4Ω·cm2. 4. In view of the slow growth rate of the GZO films at low sputtering power, a new growth method was designed. The GZO film was grown at low sputtering power(50W) to protect p-Ga N surface firstly, and then at high power(300W) to increase the growth rate. By using this method, the sputtering time can be markedly reduced. Furthermore, the thickness effect of GZO protective layer grown at low sputtering power on the performance of GZO/p-Ga N contact was studied. The specific contact resistivity of GZO/p-Ga N contacts with 10, 15 and 20 nm GZO protective layer were 3.34×10-3, 7.55×10-4 and 6.06×10-4Ω·cm2, respectively. The forward voltages of FC-LED with vias using this method are 3-3.1V at 350 m A, which meet the requirement of LED application. 5. In order to reduce cost, Cu electrode was used to replace the conventional Au electrode in OTFT. CuxS insertion layer was used as the interlayer between Cu electrode and Pentacene semiconductor to improve the contact properties. The field effect mobility of Pentacence OTFT with CuxS insert layer was 1.45cm2/V·s, which is twofold higher than conventional OTFT with Au electrodes. The improvement of device performance is attributed to the enhancement of charge-injection. The analysis of the film morphology shows that the CuxS particles are much smaller than Cu and Au particles. The small CuxS particles are easy to fill the pentacene crystal boundary resulting in better interface contact. X-ray photoelectron spectroscopy revealed that sulfate ions and copper oxide were formed during deposition, which is also considered to be responsible for the improvement.