磷化銦奈米元件對光與氣體增益研究

Abstract

近年來，由於電子元件尺度從微米數量級縮小至奈米數量級，因此在這兩種元件尺度的接點面積將會有2~3個數量級的差距，這也可能導致奈米元件的接點電阻比傳統元件的接點電阻大100~1000倍，並且接點電阻也可能會對整個元件的電阻值有所貢獻。本實驗中，磷化銦奈米線是藉由溶液-液相-固相成長法製備而成，並且將平均直徑與長度分別約為20 nm及2-5 μm的磷化銦奈米線存放於甲苯溶劑中儲存，再藉由標準電子束微影技術製作兩點量測的磷化銦奈米元件。為了改善接點電阻及縮小元件的室溫電阻值，我們會在進行觀察元件的電流-電壓行為之前，先將所有製備好的奈米元件在高真空下進行熱退火，其中溫度與時間條件為400 °C持續1分鐘。我們觀察到雖然元件裡的磷化銦奈米線是從相同溶液中擷取出，而且奈米元件的幾何結構也是固定不變地，但其室溫電阻值變化卻相當地大。我們推測室溫電阻值的差異是來自於接點電阻貢獻所致。藉由電阻對數-溫度倒數圖，奈米線主導電性元件及接點電阻主導電性元件可清楚地被分辨出來。熱活化傳輸理論可以用來解釋高溫處傳輸行為，在低溫處實驗數據則可用變程跳躍傳輸理論來加以說明。此外，我們也發現當元件室溫電阻越大時，熱活化傳輸理論所擬合的範圍會越小，這意味著接點電阻隨著室溫電阻的上升將逐漸地主導整個元件的電阻。另一方面，在照光與曝氧的實驗中，我們發現無論是奈米線或接點電阻所主導的奈米元件皆會有電阻的變化。令人訝異的是接點主導電性元件在照光或曝氧後的電阻變化率會比磷化銦奈米線主導電性元件大的許多。

The dimension of electronic devices are reduced further and further from micrometer to nanometer scale and the electrical contact area is squeezed in size by 2-3 orders of magnitude. As a consequence, the contact resistance of nanoscale devices could be hundred or thousand times larger than that of conventional devices and dominant to the total resistance of devices. Indium phosphide (InP) nanowires were synthesized by using a self-seeded, solution-liquid-solid growth method and were stored in a toluene solvent. InP nanowires are ~ 20 nm in diameter and 2-5 μm in length. By using a standard electron-beam lithography technique, two-probe InP nanodevices were fabricated. In order to improve the electrical contact and to diminish the total resistance, all of InP nanowire devices were annealed at 400 °C in a high vacuum for 1 min before measurements of current-voltage curves. The room-temperature resistance of these devices varied considerably although the InP nanowires were picked up from the same source and the dimensions of the nanowires and devices were kept the same. It was conjectured that the difference of room-temperature resistance comes from the contribution of contact resistance. According to the temperature behaviors, the nanowire devices can be categorized into nanowire- and contact-dominated ones. The temperature dependent resistance follow the thermally activated and variable range hopping transport at high and low temperatures, respectively. Moreover, as for high room-temperature resistance devices, the temperature range of resistance following the thermally activated transport shrinks, implying that the contact is deteriorated and dominant to the total resistance. On the other hand, both nanowire- and contact-dominated devices were exposed to light and oxygen gas to see any different responses. Surprisingly, in comparison with the nanowire-dominated devices, the contact-dominated devices always exhibit a much higher ratio of resistance changes in response to either light or oxygen gas exposures.