(111) 실리콘 기판 위에 성장된 GaN 박막의 쇼트키 접촉 특성
Characteristic of schottky contact on GaN epitaxial layer grown on (111) silicon
반도체 다이오드 실리콘;
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Silicon is an attractive substrate for III-nitride epitaxy, because the extensive area is available at a significantly low cost. Since there are thermal mismatch as well as the lattice structure difference, it is not available to control the cracks on whole wafer perfectly by the process parameters. In this sense, to achieve the electronic devices on the partially cracked nitride layers, it is essential to investigate the contact properties on the cracked GaN surfaces. Metal-semiconductor contacts properties were investigated by fabricating a schottky diode on the cracked GaN layer grown on p-type (111) silicon substrate. characteristics of the fabricated Pt/schottky diodes of different diameters was measured. They had effective barrier height of around 0.67eV and ideal factor of 4.2. Compared to the GaN schottky diode on sapphire substrate, the fabricated one has lower barrier height. The forward logI-V characteristics of schottky diodes do not exhibit uniform linearity as well. It is thought that, because of the cracks in GaN epi-layeron silicon, there can be non-ideal current mechanisms which are effectively parallel with the intrinsic GaN schottky diode. They might be parasitic Pt-silicon schottky diode and/or crack induced surface conduction. In the reverse I-V curve, it shows an acceptable increase of the reverse leakage current according to the reverse bias as a rectifier. And the reverse breakdown voltage is 5∼10 V above which the leakage current increases markedly. And by further bias, it shows effectively ohmic behavior. Considering the previous report, it is very promising to apply the cracked AlGaN/GaN layer to the fabrication HFET's. The transmission line method(TLM) measurement was demonstrated for the ohmic contacts on the GaN layer on (111) silicon wafer. We used Ti/Al/Ni/Au multi-layers and annealed in N₂ ambient at 700℃ for 30s for ohmic metal. Because of the random distribution of the cracks and random direction of them, the plot has non-linear points. The contact resistivity was 5.51×10^(-5) Ω㎠. The I-V curve between two contact pads, which clearly shows ohmic properties of them. We measured the spectral responsivity of the fabricated schottky diode. We got the cutoff wavelength of 360 nm, peak responsivity of 0.097 at 300nm, and UV/visible rejection ratio of about ∼10², which shows potential applicability to the opto-eletronic devices. In conclusion, even though there is significant crack density in the GaN layer on silicon, we successfully achieved the schottky diode. The result gives a positive signal to apply the cracked GaN layer on silicon subatrate to the HFET's and integration of the electronic devices.