Under identical preparation conditions, Au/ GaN Schottky contacts were prepared on two kinds of GaN epilayers with significantly different background electron concentrations and mobility as well as yellow emission intensities. Current-voltage ͑I-V͒ and variable-frequency capacitance-voltage ͑C-V͒ characteristics show that the Schottky contacts on the GaN epilayer with a higher background carrier concentration and strong yellow emission exhibit anomalous reverse-bias I-V and C-V characteristics. This is attributed to the presence of deep level centers. Theoretical simulation of the low-frequency C-V curves leads to a determination of the density and energy level position of the deep centers. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2358207͔In the past decade, GaN and related III-nitride compounds have attracted a great deal of interest because of their wide optoelectronic and electronic applications, such as blue/ ultraviolet light-emitting diodes, ultraviolet detectors, laser diodes, and high-temperature/high-power transistors. MetalGaN contacts including Schottky contacts are of great importance for device applications of GaN-based materials. Despite the commercialization of GaN-based bright lightemitting diodes and even laser diodes, 1 a number of issues related to metal-GaN contacts ͑especially Schottky contacts͒ still remain. These are not well understood and are thus being actively investigated.2-8 Having a work function of ϳ5.1 eV, gold ͑Au͒ is one of the most used metals in the fabrication of metal-semiconductor Schottky and Ohmic contacts. For Au/ GaN Schottky contacts, several groups have reported their results.2,3,5 However, few studies have been reported to investigate the influence of deep level centers ͑which are closely associated with the yellow emission band͒ on the capacitance-voltage characteristics of metalGaN Schottky contacts. In this letter, we show experimentally that the deep level centers located at about 1.3 eV can lead to typical anomalous reverse-bias C-V characteristics of Au/ GaN Schottky diodes, particularly the low-frequency C-V characteristics.Two n-type GaN epilayers, namely, S1 and S2, grown on ͑0001͒ sapphire substrate by metal organic chemical vapor deposition, were used as the starting materials for the study. Using standard Hall measurements, the electron concentration and mobility of samples S1 and S2 at room temperature were determined to be 1.9ϫ 10 17 cm −3 and 331 cm 2 V −1 s −1 , as well as 3.3ϫ 10 16 cm −3 and 836 cm 2 V −1 s −1 , respectively. Prior to making metal contacts, the samples were cleaned by immersing the samples sequentially in boiling acetone and ethanol and de-ionized water. To remove any native oxide and contamination, they were dipped into different acid solutions after which the samples were rinsed in de-ionized water and dried with N 2 . Au and indium ͑In͒ were used to make Schottky and Ohmic contacts, respectively. I-V measurements were carried out using an HP 4155A parameter analyzer, and frequency-dependent C-V characteristics of the...
A nano-floating gate memory structure based on Ni nanocrystals (NCs) embedded HfOx film is deposited by means of radio-frequency magnetron sputtering. Microstructure investigations reveal that self-organized Ni-NCs with diameters of 4-8 nm are well dispersed in amorphous HfOx matrix. Pt/Ni-NCs embedded HfOx/Si/Ag capacitor structures exhibit voltage-dependent capacitance-voltage hysteresis, and a maximum flat-band voltage shift of 1.5 V, corresponding to a charge storage density of 6.0 × 1012 electrons/cm2, is achieved. These capacitor memory cells exhibit good endurance characteristic up to 4 × 104 cycles and excellent retention performance of 105 s, fulfilling the requirements of next generation non-volatile memory devices. Schottky tunneling is proven to be responsible for electrons tunneling in these capacitors.
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