砷離子佈植砷化鎵光導天線產生次毫米波的綜合研究

Abstract

由於砷離子佈植砷化鎵的超快光電特性,可被用來製作THz放射器。我們研究單一佈植與多重怖植光導天線的特性。後者是在砷化鎵上佈植50,100, 200KeV三種佈植能量,佈植砷離子濃度為 ions/cm 並經由600°C、30或60分鐘的退火製程。我們以反射式泵探系統量測此材料載子生命期約為幾個皮秒。更重要的是,退火過程使大部份晶格恢復,並有微小砷凝聚生成,降低此材料的暗電流,避免在高壓下的崩潰效應。因此,以此材料製作的光導天線可以加高壓產生高功率的次毫微米波。在THz量測系統方面,利用光脈衝寬約100fs、波長在0.8μm附近的被動鎖模鈦藍寶石雷射為光源,經過電光晶體碲化鋅的電光取樣系統來量測光導天線所產生的次毫微米波。我們製作(20μm ~ 1mm)各種不同型式的光導天線,發現其在時域與頻域上有顯著的差異。我們將此結果與之前做於半絕緣砷化鎵與低溫分子束磊晶成長砷化鎵比較。

The ultrafast optoelectronic characteristics of arsenic-ion-implanted GaAs indicate that they could be attractive candidates as THz emitters. We have studied the characteristics of photoconductive antennas fabricated on single- and multi-energy arsenic-ion-implanted GaAs. The latter samples were implanted with 50, 100, 200 keV arsenic ions at ions/cm2 and furnace-annealed at 600°C for 30 or 60 minutes. The carrier-trapping times of the samples are of the order of a few picoseconds as determined from time-resolved reflectivity measurements. Further, the annealing process reduces the dark currents of the ion-bombarded GaAs to those comparable to semi-insulating GaAs or better (less than 1 nA at bias of 30 V). As a result, antennas fabricated on these photoconductors can be biased at high voltages. Both dipole and large area-antennas have been fabricated. Optically - excited THz radiation from these devices were coherently detected using electro-optic sampling [1]. Significant difference in temporal and spectral characteristics of terahertz radiation emitted by antennas of different gap sizes (20μm ~ 1mm) is reported. The results are compared to previous works on THz antennas fabricated on S. I. GaAs and low-temperature MBE-grown GaAs (LT-GaAs) [2-4].