High Performance Optoelectronic Integrated Devices by Micromachining Technique

其中光接收和光发射器件垂直地和直接地集成的光电集成器件产生对于光信号处理和光互连重要的各种新的光学功能。通过垂直和直接集成传统的光电子器件，不仅可以获得组成器件的综合特性，而且由于它们之间的相互作用，可以容易地获得新的功能。这导致更一般的工程概念，即集成度越高，设备的功能越高。基于这一概念，我们首先把多个激光二极管和异质结光电晶体管集成在一起，利用内部的光电耦合，研制出了具有多种触发器功能的先进光逻辑器件，如双稳态、三稳态触发器和无稳态多谐振荡器等。这种集成器件在并行信号处理中的应用，是非常有意义的 ...更多信息 重要的是拥有表面发射功能。近年来，垂直腔面发射激光器（VCSEL）引起了人们的广泛关注。然而，当我们使用VCSEL作为集成器件的激光器部分时，从VCSEL到异质结光电晶体管的光反馈变得太强，因为激光输出功率直接进入光电晶体管。集成器件利用自发辐射代替激光辐射作为光反馈，实现各种功能。强的光反馈导致诸如光开关的功能的数量有限。为了避免这种限制，我们已经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，并且一部分光耦合出到垂直于衬底表面的方向。因此，当我们在没有光栅耦合器的位置上集成光电晶体管时，反馈光变成自发光，可以预期各种功能。本工作首次实现了适合于集成的嵌入式光栅耦合器的圆光栅耦合面发射激光器的激射振荡。然而，从器件的近场图案观察，发现激光主要沿着[110]方向观察，并且图案倾向于随着注入电流的增加而扩展到更宽的区域。为了克服上述问题，我们采用了一种新的方法，即晶片熔接技术来嵌入光栅。该过程的基本思想如下：准备两个外延晶片A和B（晶片A具有分离限制多量子阱结构，晶片B具有二阶衍射光栅），每个晶片的表面用缓冲HF溶液预处理，在高于1.7N/cm ^2的压力下堆叠晶片，并在620 ℃下在H_2气氛中加热30分钟。然后晶片A和B被牢固地结合以承受各种工艺，通过SEM和TEM观察发现，在器件中形成了均匀的空气/半导体光栅，其深度和周期分别约为0.2 μ m和0.4 μ m。由于质量输运现象，反应离子刻蚀得到的矩形光栅形状变成了有点圆形。在质量输运的帮助下，熔融界面变得更牢固，电性更可靠。还发现，晶片熔合后光栅的形状几乎不依赖于晶体取向。然后将熔融晶片加工成脊形波导结构，并在室温下成功地实现了连续激光振荡。这些结果对于开发均匀嵌入圆光栅耦合面发射元件的集成器件是非常鼓舞人心的。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