Engineering the gain-bandwidth product of phototransistor diodes.
Engineering the gain-bandwidth product of phototransistor diodes.
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DOI：
10.1063/1.5095815
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发表时间：
2019-07
影响因子：
4
通讯作者：
S. Bianconi;M. Rezaei;Min-Su Park;Wenyuan Huang;C. Tan;H. Mohseni
中科院分区：
文献类型：
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作者：
S. Bianconi;M. Rezaei;Min-Su Park;Wenyuan Huang;C. Tan;H. Mohseni
近年来，光电晶体管大大扩展了其应用领域，包括外差检测和光学互连等。与低光成像不同，其中一些应用需要能够在相对高光水平下工作的快速光电探测器。由于光电晶体管的增益和带宽在不同的光功率下并不是恒定的，因此针对低光水平操作进行优化的器件无法有效地用于不同的技术应用。我们对短波长红外光电晶体管的增益和带宽作为我们设计和制造的三种器件架构的光功率水平的函数进行了广泛的研究。发现光电探测器的增益随着载流子注入的增加而增加。基于 Shockley-Read-Hall 复合模型，我们表明这是由于光电晶体管基层中复合中心的饱和造成的。最终，在较高的光照水平下，由于柯克效应，增益会下降。由于这些相反的机制，增益带宽积在给定功率水平处达到峰值，这取决于器件设计和材料参数，例如掺杂和缺陷密度。在这种物理理解的指导下，我们设计并演示了一种光电晶体管，它能够为高速应用提供高增益带宽积。所提出的设计标准可以与器件尺寸工程结合使用，以实现增益和带宽的广泛可调性，从而为不同光水平应用的快速光电探测器铺平道路。
In recent years, phototransistors have considerably expanded their field of application, including for instance heterodyne detection and optical interconnects. Unlike in low-light imaging, some of these applications require fast photodetectors that can operate in relatively high light levels. Since the gain and bandwidth of phototransistors are not constant across different optical powers, the devices that have been optimized for operation in low light level cannot effectively be employed in different technological applications. We present an extensive study of the gain and bandwidth of short-wavelength infrared phototransistors as a function of optical power level for three device architectures that we designed and fabricated. The gain of the photodetectors is found to increase with increasing carrier injection. Based on a Shockley-Read-Hall recombination model, we show that this is due to the saturation of recombination centers in the phototransistor base layer. Eventually, at a higher light level, the gain drops, due to the Kirk effect. As a result of these opposing mechanisms, the gain-bandwidth product is peaked at a given power level, which depends on the device design and material parameters, such as doping and defect density. Guided by this physical understanding, we design and demonstrate a phototransistor which is capable of reaching a high gain-bandwidth product for high-speed applications. The proposed design criteria can be employed in conjunction with the engineering of the device size to achieve a wide tunability of the gain and bandwidth, hence paving the way toward fast photodetectors for applications with different light levels.