氮摻雜超奈米晶鑽石膜光性與電性傳導研究

Abstract

本實驗主要研究微波輔助化學氣相沉積(MPECVD)成長的氮摻雜超奈米晶鑽石膜(N-doped UNCD)的導電機制。利用拉曼光譜分析成長得到的N-doped UNCD，可得到明顯的D、G band以及1150cm-1的UNCD特徵峰。然而藉由PL光譜分析時，卻看不見Nitrogen vacancy的放光，因此初步推測氮並無進入晶粒，而是存在於晶界。我們將試片做霍爾量測，證明其為N型半導體，其載子濃度高達1019~1020/cm3，從場效電晶體(Field Effect Transistor)的量測裡可以得知，電性並不受閘極偏壓影響，因為其摻雜濃度過高，晶界比例上升，大大提升N-doped UNCD的導電度，使其擁有類金屬特性。最後從變溫電性量測中得知，此一N-doped UNCD薄膜在溫度在220K以上電子傳導是透過熱傳導，溫度220K以下是透過跳躍方式在導電，而傳導的機制是Mott`s Hopping (m=3+1)三維跳躍模式進行，而傳導的自由電子則是在晶界中C━N σ*、C━N π*、C─N σ*所提供。

In this study, the conduction mechanism of nitrogen-doped ultranano crystalline diamond films (N-doped UNCD) grown by microwave-assisted chemical vapor deposition (MPECVD) was investigated. From Raman spectroscopy analysis, the N-doped UNCD film shows significant D, G band and the 1150cm-1 characteristic peaks. From photoluminescence measurements we found no characteristic light emission of the nitrogen vacancy in the PL spectra of N-doped UNCD films. Therefore, the doped nitrogen atoms did not enter the grains, but only existed in the grain boundary. From the Hall measurement, the N-doped UNCD film was proven to be heavily doped n-type semiconductor with a carrier concentration as high as 1019 ~ 1020/cm3. Furthermore, we fabricated a field effect transistor (FET) structure on the N-doped UNCD film. From the transconductance measurements, we found that the electrical conductivity of N-doped UNCD film could not modulated by the gate bias. Such results are attributed to the high carrier concentration and the metallic conduction behavior of N-doped UNCD films. Finally, from the variable temperature electrical measurements, we conclude that the N-doped UNCD films exhibit thermionic conduction at a temperature above 220K. At a temperature below 220K, the hopping conduction is responsible for the carrier transport and it can be modeled with Mott `s hopping model where the free conducting electrons are provided from the grain boundaries C=N σ *, C=N π *and C-N σ * .