我們展示了一種新穎的近彈道單載子傳輸光電二極體(Near-Ballistic Uni-Traveling-Carrier Photodiode，簡稱NBUTC-PD)結構，該結構具有內切式的載子收集層。在內切式收集層結構中，由於吸收層的寬度更大，可以提高響應度、輸出射頻功率和飽和光電流。與主動區直徑3µm的元件相比，內切式收集層結構的元件(11µm)具有更高的響應度( 0.11 vs. 0.1 A/W )、更高的輸出功率( 0.4 vs. -2.4 dBm@165GHz )以及更高的飽和光電流( 9 vs. 7mA )。另外，內切式收集層的結構可以有效地降低接面電容，可以最大限度地減少因吸收層面積增加而導致的頻寬下降，與主動區直徑3µm的元件相比，內切式收集層結構的元件(11µm) 頻寬只降低了65 GHz (220 GHz 與 285 GHz)。總結來說，我們新提出的內切式的載子收集層結構能有效解決近彈道單載子傳輸光電二極體(NBUTC-PD)中，元件頻寬與元件輸出特性(輸出射頻功率、輸出光電流)之間的相互限制。;We demonstrate a novel Near-Ballistic Uni-Traveling-Carrier Photodiode (NBUTC-PD) structure with an undercut profile of collector layer. By using undercut collector structure in a InP based uni-traveling carrier photodiode (UTC-PD), it’s responsivity, output RF power and saturation photocurrent can be improved due to the larger width of p-type absorption region. Furthermore, the undercut profile in collector layer, can effectively reduce the junction capacitance and minimize the bandwidth degradation due to the increase of active area of absorption region. Higher responsivity (0.11 vs. 0.1A/W), output power (0.4 vs. -2.4 dBm@165GHz) and saturation photocurrent (9 vs. 7mA) of undercut collector device (11µm) as compared to those of references with miniaturized diameters (3µm) has been demonstrated. Compared with directly downscale device (3µm), undercut collector structure device (11µm) exhibit less bandwidth degradation (220GHz vs. 285GHz). In conclusion, the demonstrated device structure can effectively overcome the trade-off between bandwidth and MMW saturation power (current) in THz photodiode.
