低耗能之砷化鎵極紫外光至紅外光極寬波段光偵測器之研究

Abstract

本論文以三五族半導體材料-砷化鎵為研究主軸，搭配金屬材料產生熱電子，以製作蕭特基二極體之光偵測器，研究成果是將砷化鎵光感測器延伸至近紅外光通訊波段之偵測，並研究砷化鎵與金屬材料在極紫外光波段的光學性質，並應用於極紫外光波段之光偵測，證實同一個元件即可以展現從極紫外光到近紅外光波段之寬波段偵測能力。

論文第一部分(第三章)，藉由正面照射式元件架構，提升金與鉬金屬薄膜於砷化鎵深溝槽結構的光學特性，使其能夠在近紅外光通訊波段產生低反射、高吸收之特性，使砷化鎵基材突破直接能隙870 nm (1.42 eV)的限制，得以延伸其偵測段段到光通訊波段1310奈米及1550奈米。以鉬結構元件為例，在1310 nm及1550 nm之光電流響應度分別為0.27 mA/W以及0.16 mA/W，相較於金矽基結構元件小了一個數量級。然而以光電壓偵測的方式，鉬結構元件在1310 nm及1550 nm之光電壓響應度分別為577.47(V/W)以及435.15(V/W)，相較於矽基近紅外光元件之光電響應度(10 mV)大了一萬倍。實驗結果推斷光電壓響應模式顯著的原因是因為當微小的熱載子光電流流經高阻值及高陷阱密度之砷化鎵基板時，會產生顯著的光電壓壓差。 論文第二部分(第四章)提出背面照射式之光通訊波段偵測器，相較於正面入射式，背面入射式元件主要有三個優點: (1)熱載子有效產生且有效收集、(2)寬波段高吸收(可同時涵蓋1310 nm及1550 nm)、(3)元件對光入射角度不敏感。實驗結果驗證其光電流與光電壓響應度較正面入射式之元件來的好，以鉬結構元件為例，背面入射式之光電流響應度於1310 nm及1550 nm分別為0.95 mA/W以及0.25 mA/W，而光電壓響應度為781.52(V/W)以及540.96(V/W)，相較於第三章之正面入射光電流響應度於1310 nm及1550 nm分別提升3.5倍及1.66倍；而光電壓響應度於1310 nm及1550 nm分別提升1.35倍及1.24倍，本論文之砷化鎵光偵測器成功延伸至近紅外光波段偵測。 論文第三部份(第五章)，透過光學分析，找到鉬金屬適合在極紫外光波段下當作蕭特基光偵測器的正面電極，因為鉬在13.5 nm的波段下具有高穿透特性，此外砷化鎵材料相較於矽基半導體具有非常大的吸收係數，因此認為鉬搭配砷化鎵材料之蕭特基二極體有機會作為良好的極紫外光的光偵測器。成功的將第三章節所製作的元件延伸至EUV波段偵測，證實本論文之砷化鎵光感測器可以展現從極紫外光到近紅外光波段之寬波段偵測能力。然而，在極紫外光波段所產生之光電流僅有10-9安培，相較於商用極紫外光感測器都小上許多，可能是高阻值砷化鎵基板並不適合當作基材。為了進一步增加偵測效率，未來改善之研究預期採用磊晶的方式製作高品質之砷化鎵薄膜，並以利用離子佈值的方式改變砷化鎵薄膜的載子濃度，以調控砷化鎵薄膜的電子遷移率以及與金屬接面之空乏區大小與內建電場分布。

In this thesis, we study gallium arsenide (GaAs) and hot electron based Schottky diode of photodetector performing broadband detection capability working from extreme ultraviolet (EUV) to near-infrared (NIR) regime. This study demonstrated the hot electrons generated in structured gold (Au) or molybdenum (Mo) electrodes and propagating to metal/ semiconductor (GaAs) junction can be used for optical-electrical signal conversion for detecting light with photon energies below the bandgap of the semiconductor, especially in the spectral regime for optical telecommunication. Furthermore, we investigated the optical properties of GaAs and metal films in the EUV spectral regime to demonstrate a low power consumption of photodetector having an ultra-broadband detection ability. In the first part of this thesis, metal (Au, Mo)/ semiconductor (GaAs) based Schottky junction photodetector has been designed for hot electron collection from deep-trench/ thin metal (DTTM) based active antenna which takes the advantage of surface plasmon resonance and three-dimensional cavity effects. The DTTM-based devices have attractive properties of low reflection and high absorption in the near-infrared (NIR) regime, which enables the GaAs based devices breaking the limitation of bandgap of 870 nm (1.42 eV), extending its detection capability to the spectral regime of optical communication wavelengths of 1310 nm and 1550 nm. Taking the Mo/GaAs DTTM device as an example, the photocurrent responsivities at 1310 nm and 1550 nm are 0.27 mA/W and 0.16 mA/W, respectively, which is an order of magnitude smaller than that of the Si-based DTTM device. However, in terms of photovoltage detection, the response of the Mo/GaAs DTTM device at 1310 nm and 1550 nm are 577.47 (V/W) and 435.15 (V/W), respectively, which is 10,000 times larger than the photoelectric response of a Si-based DTTM device. We suggested that the photovoltage responsivity is significant for the high resistance and trap density of GaAs substrate. In the second part of this thesis, the concept of backside-illuminated schemes of metal (Au or Mo) film along with GaAs based DTTM structure were proposed. Compared with the front-illuminated devices, the backside-illuminated devices have three main advantages: (1) Hot carriers could be effectively generated and effective collection. (2) Devices performed broadband absorption covering the wavelengths of 1310 nm and 1550 nm, (3) Devices performance were not sensitive to the angle of incident performing omnidirectional detection properties. The measured results demonstrated that the responsivity of photocurrent and photovoltage are much higher than those of the front-illuminated devices. In the case of Mo/GaAs DTTM device, the photocurrent responsivity of the back-illuminated type are 0.95 mA/W and 0.25 mA/W at 1310 nm and 1550 nm, respectively, and the photovoltage responsivity are 781.52 (V/W) and 540.96 (V/W), respectively. In the third part of this thesis, because of high transmission at the wavelength of 13.5 nm, we suggested Mo is a suitable metal as the front electrode of Schottky photodetectors in the EUV spectral regime. Moreover, GaAs has a high absorption coefficient compared to Si in the EUV regime. Therefore, it is considered that Mo/GaAs-based Schottky diodes have a good opportunity to be used as a superior photodetectors working in EUV regime. In this study, we extended the Mo/GaAs DTTM devices operating in the EUV regime. Because of high resistance of GaAs substrate, the generated excess photocurrent in the EUV regime is much smaller than that of the Si-based photodetector.