在低溫下磷化銦異質接面雙極性電晶體之直流特性分析

Abstract

隨著通訊技術的發展，對5G毫米波放大器的需求不斷增加，並展望未來6G太赫茲應用，磷化銦（InP）被視為極具潛力的半導體材料。磷化銦具備高熱導率、高電子遷移率及低能隙，使用磷化銦與砷化鎵銦(InGaAs)或銻砷化鎵(GaAsSb)製成的異質接面雙極性電晶體（HBT）具有較低的表面複合速度，可縮小尺寸並降低耗電量。將磷化銦異質接面雙極性電晶體應用於低地軌道衛星也具備巨大前景，其高頻性能適用於從GHz至太赫茲波段的衛星通信，並且其高功率輸出增強了傳輸功率和信號覆蓋。磷化銦異質接面雙極性電晶體還具有優異的熱導率、熱穩定性和抗輻射能力，可在低地軌道衛星中保持穩定的性能。 本研究對InP/ GaAsSb/ InP雙異質接面雙極性電晶體（DHBT）進行了多項直流特性分析。首先，我們使用濕蝕刻方法製造異質接面雙極性電晶體的射極、基極和集極高台部分。濕蝕刻可以有效減少蝕刻過程中產生的副產物。在射極部分，我們設計了三種尺寸，分別為50×50、60×60、70×70μm²，以探討射極尺寸對直流特性的影響。結果顯示，射極尺寸較小的元件具有較大的電流增益和較小的偏移電壓。隨後，我們在元件上生長了一層SiN作為鈍化層，並比較鈍化前後的特性差異，發現鈍化後，元件的漏電流增加，電流增益降低，偏移電壓變大。 當將磷化銦異質接面雙極性電晶體應用於衛星通信時，必須考慮其在低溫下的性能特性，因為低軌域衛星的環境溫度會低至¬-100度C以下。本研究利用低溫系統並加入氮氣，測量磷化銦異質接面雙極性電晶體在300K至77K範圍內的直流特性，結果顯示，當元件處於77K的低溫環境時，仍能保持電晶體的特性，且溫度越低，電流增益越大、漏電流越小，然而，低溫下的缺點是偏移電壓較大。 本研究利用ADS（Advanced Design System）建立模型，建立射極尺寸為50×50μm²在溫度為300K時的模型。我們將比較量測結果與模型生成的直流特性，最終求出一個包含溫度變數的跨導（transconductance）以及漏電流的公式，此公式能描述本研究製作的磷化銦異質接面雙極性電晶體的特性。

With the advancement of communication technology, the demand for 5G millimeter-wave amplifiers continues to grow, and future applications in 6G terahertz technology are anticipated. Indium Phosphide (InP) is regarded as a highly promising semiconductor material. InP possesses high thermal conductivity, high electron mobility, and a low bandgap, making it suitable for low-voltage operations. Heterojunction Bipolar Transistors (HBTs) made from InP and Indium Gallium Arsenide (InGaAs) or Gallium Arsenide Antimonide (GaAsSb) have lower surface recombination velocities, allowing for smaller device sizes and reduced power consumption. Applying InP HBTs to Low Earth Orbit (LEO) satellites also holds significant potential. Their high-frequency performance, suitable for GHz to terahertz band satellite communications, along with high power output, enhances transmission power and signal coverage. Additionally, InP HBTs offer excellent thermal conductivity, thermal stability, and radiation resistance, ensuring stable performance in LEO satellite environments. This study analyzes the DC characteristics of InP/ GaAsSb/ InP Double Heterojunction Bipolar Transistors (DHBTs). First, we fabricated the emitter, base, and collector mesas of the HBTs using a wet etching method. Wet etching effectively reduces by-products generated during the etching process. For the emitter, we designed three sizes: 50×50, 60×60, and 70×70 μm², to investigate the impact of emitter size on DC characteristics. The results show that devices with smaller emitter sizes exhibit higher current gain and lower offset voltage. Subsequently, a layer of SiN was grown on the devices as a passivation layer, and the characteristics before and after passivation were compared. It was found that after passivation, the leakage current increased, the current gain decreased, and the offset voltage became larger. When applying InP HBTs to satellite communications, it is essential to consider their performance characteristics at low temperatures, as the environmental temperature in low Earth orbit satellites can drop below -100°C. This study utilized a low-temperature system with nitrogen gas to measure the DC characteristics of InP HBTs within the 300K to 77K range. The results show that at 77K, the devices retain their transistor characteristics, and as the temperature decreases, the current gain increases while the leakage current decreases. However, a drawback at low temperatures is the larger offset voltage. In this study, we used ADS (Advanced Design System) to build a model for an emitter size of 50×50μm² at a temperature of 300K. We will compare the measured results with the DC characteristics generated by the model. Ultimately, we aim to derive a formula for transconductance and leakage current that includes temperature variables, describing the characteristics of the indium phosphide heterojunction bipolar transistor fabricated in this study.