用熱還原氧化石墨烯探索強場下電子電洞對產生之機制

Abstract

本實驗用熱還原氧化石墨烯探索其在電性下傳輸機制，利用兩點量測法，量測電性傳輸及調控背向閘極偏壓，根據小場下室溫電導率，推測氧化石墨烯氧覆蓋率，本實驗的氧化石墨烯氧覆蓋率大約在16%~18%，根據以往實驗室所量測的實驗數據，氧化石墨烯在小電場不同溫度下的電阻值，可用Mott’s 2D VRH擬合，本實驗嘗試探討高電場的傳輸行為，因此在80 K，使用電場趨動的變程式跳躍傳輸Shklovskii expression擬合分析，其擬合結果不好，其因在Shklovskii expression適用於T=0 K，因此加入溫度修正項去擬合，得知在低溫時，其熱還原氧化石墨烯為電場趨動的變程式跳躍傳輸，然而電流密度在80K與300K上升速率不同，因此本實驗假定300K為power law關係，並以Schwinger mechanism模擬分析，在強場量測下，氧化石墨烯其電性由線性傳輸到非線性傳輸，因此本實驗定義尋找轉折電場(E_c)的方法，發現其樣品E_c≈〖10〗^6 (V/m)，根據Schwinger mechanism，電子電洞對傳輸發生在中性點，若將非中性點電流密度扣除中性點電流密度，則其電性傳輸符合為歐姆定律，所以本實驗皆建立在中性點探討電子電洞對的行為，之後根據次方項的分析，雜質產生的飽和電流分析，以及理論的預測，近一步推論出模型圖，由實驗所計算出電場次方項與理論預測電場次方項一致，因而得知氧化石墨烯在強場下其傳輸機制為Schwinger mechanism。

This experiment use reduced graphene oxide (RGO) to explore transport mechanism and use two probe measurements to measure electrical properties. The oxygen coverage of RGO could be estimated by the conductivity at room temperature. In this experiment, RGO oxygen coverage ratio is about 16%～18%. According to previous work, RGO is well described by 2D VRH in low electric field. This experiment try to study transport properties in high electric field. At 80 K, the J-E curve of RGO cannot be well described by Shklovskii expression since Shklovskii expression is derived at T = 0 K. After considering the temperature factor, the J-E curve of RGO can be fitted well. However, the J-E curve at 300 K did not follow the same model prediction. In this work, we found that the J-E curves make a transition from linear to nonlinear, power law dependences. We also determined the critical field (E_C) for the transition to be E_C≈〖10〗^6 (V/m). According to Schwinger mechanism, the electron-hole pairs is produced near the charge neutrality point. From to a series experiments and analysis, we explored the electric field behavior and compared experiments with the theoretical model. The electric field behavior shows a power law dependence that is in agreement with the theoretical prediction given by J. Schwinger.