氧離子佈植砷化鎵光導天線之THz輻射特性

Abstract

本論文討論在兩組多重氧離子佈植砷化鎵 ( 2.5 X 10^13 ions/cm^2 (500 KeV & 800 KeV ), 4 X 10^13 ions/cm^2 (1200 keV ) 和 6 X 10^13 (500 keV & 800 keV ), 1 X 10^14 ions/cm^2 (1200 keV ))薄膜材料，以此製作的偶極天線兆赫波的放射特性。 利用光脈衝寬約100飛秒、中心波長為800奈米的鎖模雷射激發氧離子佈植砷化鎵光導天線，與砷離子佈植砷化鎵光導天線(~60KV/cm)比較，前者可操作在較高的電場上(~110KV/cm)放射出高功率的兆赫波訊號，且具有較高的飽和光激發能量(~45mW)。此外，改變光導天線的偶極長度也會影響到輻射波強度。該天線最大發射頻寬達1.6THz，訊噪比最佳可達到~10000以上。 最後，我們比較低溫成長砷化鎵與多重氧離子佈植砷化鎵偶極天線在輻射兆赫波上的差異性。在相同的光激發能量及電場下，我們發現後者可發射出較高的兆赫波訊號，強度(~0.17uW)約比低溫成長砷化鎵(~0.09uW)大上近一倍。雖然在頻寬上多重氧離子佈植天線和低溫成長砷化鎵天線還具有一段的差異，但由於多重佈植的方式在製程上比低溫成長來得更經濟，而且我們可以再去改變離子佈植濃度和退火溫度獲得更好的效果，因此在兆赫波的應用上還是具有相當的潛力。

THz wave was generated from dipole antenna-type devices made by using Oxygen-ion implanted GaAs. We compared the emission properties of GaAs:O photoconductive (PC) antennas with different fabricated condition ( 2.5 X 10^13 ions/cm^2 (500 KeV & 800 KeV ), 4 X 10^13 ions/cm^2 (1200 keV ) 和 6 X 10^13 (500 keV & 800 keV ), 1 X 10^14 ions/cm^2 (1200 keV ))in the pulse mode. The absolute power of THz wave was also measured by a bolometer for comparison of the relative radiation power. High breakdown voltage threshold biasing (>110KV/cm) and large saturation optical pumping power (~45mW) in multi-GaAs:O based PC antennas are reported. THz radiation power is proportional to the effective antenna length and photocurrent. We also compared the material multi-GaAs:O with low-temperature (LT) grown GaAs based on the same structure of PC antennas. The material multi-GaAs:O can generate higher THz power than LT-GaAs. It is almost 2 times higher for the GaAs:O (~0.17uW) than for the LT-GaAs (~0.09uW) under the same pump power (~35mW) and dc bias (~30V), respectively. Although the bandwidth of GaAs:O antennas is not broader than LT-GaAs, but it could be improved by optimizing the implant dosage and annealing temperature, and adopting other antenna structures for high frequency purpose. And the process of preparation for GaAs:O is easier than LT-GaAs. So it is promising as the substrate of the PC emitter antennas for THz radiation.