High Performance Optoelectronic Integrated Devices by Micromachining Technique

光电子集成器件将光接收和发光器件垂直和直接集成在一起，产生了对光学信号处理和光学互连至关重要的各种新的光学功能。通过垂直和直接集成传统光电子器件，不仅可以很容易地获得组成器件的组合特性，而且可以很容易地获得由于它们之间的相互作用而产生的新功能。这导致了更一般的工程概念，即集成度越高，设备的功能就越高。基于这一概念，我们首先通过集成多个激光二极管和异质结光晶体管，并利用内部的光电耦合，开发出具有多种触发功能的先进的光学逻辑器件，如双稳态和三稳态触发器和稳定多谐振荡器。在将集成器件应用于并行信号处理中，具有很强的…更重要的是要具备表面发射功能。近年来，垂直腔面发射激光器(VCSEL)受到了广泛关注。然而，当我们使用VCSEL作为集成器件的激光器部分时，由于激光输出功率直接进入光电晶体管，从VCSEL到异质结光晶体管的光反馈变得太强。该集成器件利用自发辐射而不是激光发射作为光反馈，以获得各种功能。强烈的光反馈导致诸如光切换之类的功能的数量有限。为了避免这一限制，我们考虑使用圆形光栅耦合表面发射器件。激光振荡发生在平行于衬底表面的方向上，并且一部分光耦合到垂直于衬底表面的方向。因此，当我们将光电三极管集成在没有光栅耦合器的位置时，反馈光变成自发光，可以预期各种功能。在这项工作中，我们首次实现了采用适合于集成的内嵌式光栅耦合器的圆形光栅耦合表面发射激光器的激光振荡。然而，从器件的近场图样观察发现，激光主要是沿[110]方向观察到的，并且随着注入电流的增加，图样有向更宽的区域扩展的趋势。为了克服上述问题，我们采用了一种新的方法来嵌入光栅，即晶片融合技术。该工艺的基本思想是：制备两个外延片A和B(晶片A具有单独的限制多量子阱结构，晶片B具有二阶衍射光栅)，每个晶片的表面经过缓冲的HF溶液处理，在高于1.7N/cm~2的压力下堆叠，并在620ﾟC的氢气气氛中加热30min，然后将晶片A和B进行牢固的键合，以承受各种工艺，扫描电子显微镜和透射电子显微镜观察发现，器件中形成了深度约为0.2微米、周期约为0.4微米的均匀的空气/半导体栅格。由于传质现象，反应离子刻蚀得到的矩形栅形变成了略呈圆形的形状。在质量传输的帮助下，熔合界面更加坚固，电子性能更加可靠。研究还发现，晶片融合后的光栅形状与晶体取向几乎没有关系。然后将熔融后的晶片加工成脊形波导结构，在室温下成功地实现了连续激光振荡。这些结果对开发均匀嵌入圆形光栅耦合表面发射元件的集成器件是非常鼓舞人心的。较少

Optoelectronic integrated devices in which light-receiving and light-emitting devices are vertically and directly integrated, produce various new optical functions important for optical signal processing and optical interconnections. By integrating vertically and directly conventional optoelectronic deices, not only the combined characteristics of the constituent devices, but also new functions due to the mutual interaction between them can be easily obtained. This leads to more general engineering concept that the higher the degree of integration, the higher the functionality of the device. Based on this concept, we have at first developed advanced optical logic devices with various flip-flop functions such as bistable and tristable flip-flops and an astable multivibrator by integrating multiple laser diodes and heterojunction phototransistors and utilizing internal optical and electrical couplings.In the application of the integrated devices to parallel signal processings, it is very … More important to possess a surface-emitting function. Recently, a vertical cavity surface-emitting laser (VCSEL) has been drawing much attention. When we use the VCSEL as the laser part of the integrated devices, however, the optical feedback from the VCSEL to the heterojunction phototransistors becomes too strong since the lasing output power directly enters the phototransistors. The integrated devices utilizes the spontaneous emission instead of the lasing emission as the optical feedback to obtain various functions. The strong optical feedback leads to the limited numbers of functions such as an optical awitching. To avoid this limitation, we have considered using a circular grating coupled surface-emitting device. The lasing oscillation occurs in the direction parallel to the substrate surface, and a part of the light is coupled out to the direction normal to the substrate surgace. Therefore, when we integrate the phototransistors on the position where there is no grating coupler, the feedback light becomes spontaneous light and various functions can be expected. In this work, we have for the first time achieved the lasing oscillation of the circular grating coupled surface-emitting laser with the embedded grating couplers which is suitable for integration. From the near-field pattern observation of the device, however, it was found that the lasing was observed mainly along the [110] direction and the pattern tended to spread into a wider area with increasing injection current. This behavior is due to a slight nonuniformity of the grating shapes in the azimuthal direction.To overcome the above problem, we have employed a new method to embed the gratings, that is, wafer-fusion technique. The basic idea for the process is as follows : two epitaxial wafers A and B were prepared (the wafer A has a separate confinement multiple quantum well structure, and the wafer B has second-order diffraction gratings), the surface of each wafer was pretreated by buffered HF solution, and the wafers were stacked under the pressure higher than 1.7N/cm^2 and heated in H_2 atmosphere for 30min at 620ﾟC.Then the wafers A and B were bonded as strong as to withstand various processes, and it was found from the SEM and TEM observation that the uniform air/semiconductor gratings were formed in the device having the depth and period about 0.2mum and 0.4mum, respectively. The rectangular-like grating shape obtained by the reactive ion etching was changed to somewhat circular shape due toe the mass-transport phenomenon. The fused interface bacame firmer and electronically more reliable with the aid of the mass-transport. It has been also found that the shape of the grating after wafer-fusion has almost no dependence on the crystalline orientation. Then the fused wafers were processed to a ridge waveguide structure, and the CW lasing oscillation has been successfully achieved at room temperature. These results are very encouraging to develop integrated devices with uniformly embedded circular grating coupled surface-emitting elements. Less