Basic Research on Optoelectronic Devices for Neural Networks

从光电子集成电路(OEIC)的角度对大规模神经网络的神经器件和光学互连进行了基础研究。研究了基本的可行性和技术障碍。其他神经元的光输出乘以突触权重，然后在人工神经元中求和。然后利用Sigmoid功能输出光输出，该功能很容易通过连接到差动放大器的LED来产生。突触连接的功能在神经元中是最重要的。首先，开发了一种光电电路，作为具有可变突触权重的突触连接。从而阐明了光互连的基本功能和较好的性能。然后开发了一种具有自组织功能的新设备，其突触权重可以根据教师的信号进行调整。这些光电子学基本器件和电路是采用硅集成电路工艺制造的。阐明了适合于大规模集成的较好的特性，如NA量级的低电流操作和结构简单。还研究了单片OEIC所需的在Si上外延生长GaAs时的初始生长机理。为了在硅上生长高质量的GaAs体，必须从根本上避免最初的三维生长。通过引入化学键较强的AlAs初始层或采用固相外延生长的较薄的GaAs层，实现了准二维生长。此外，由于增强了Ga的迁移，在(111)B和(110)的同质外延中获得了镜面。

A basic study on neuro-devices and optical interconnection has been conducted for large-scale neural networks in the viewpoint of an optoelectronic integrated circuit (OEIC). The fundamental feasibiity and technological barriers were investigated.Optical outputs from other neurons were multiplied by synaptic weights and summed in the artificial neuron. Then the optical output was emitted with the sigmoid function, which is easily generated by an LED connected to a differential amplifier. The function of synaptic connection is most important in the neuron. Firstly, an optoelectronic circuit was developed, which acted as a synaptic connection with variable synaptic weights. As a result, the basic function as well as the preferable performances of the optical interconnection were clarified. Then a new device with a self-organizing function was developed, whose synaptic weight is adapted to a teacher's signal. These optoelectronic fundamental device and circuits were fabricated using Si IC technology. Preferable characteristics for large-scale integration were clarified such as a very low current operation of the order of nA and a simple structure.Initial growth mechanisms were also studied in epitaxial growth of GaAs on Si, which could be needed for one-chip OEIC. The initial three dimensional growth must be avoided essentially for a growth of high quality GaAs on Si. A quasi-two dimensional growth was realized by introducing an AlAs initial layer having a stronger chemical bond or a thin GaAs layer grown by solid phase epitaxy. In addition, a mirror surface was obtained in homoepitaxy of GaAs(111)B and (110) by enhancing a Ga-migration.