BACKGROUND

The present invention relates to photonics chips and, more particularly, to structures including multiple photodiodes and methods of fabricating a structure including multiple photodiodes.

Infrared wavelength motion detection systems, such as Light Detection and Ranging (LIDAR) systems, may use a germanium photodiode as a sensor. A photodiode converts impinging electromagnetic radiation by the photoelectric effect into free charge carriers as photons are absorbed and electron-hole pairs are generated. Germanium exhibits high photon absorption in the infrared wavelength range and in the visible wavelength range. Conversely, silicon photodiodes exhibit high photon absorption in the visible wavelength range but poor photon absorption in the infrared wavelength range.

The ability of a photodiode to generate free charge carriers depends, among other factors, on the bandgap of the light-absorbing material from which the photodiode is constructed. The bandgap is the distance between the valence band of electrons and the conduction band in the electronic band structure of a material. Essentially, the bandgap represents the minimum energy that is required to excite an electron from the valence band to a state in the conduction band. In general, a material having a lower energy bandgap has a higher absorption coefficient at a particular wavelength. Silicon is an inefficient photodiode material for infrared wavelengths due to its large bandgap. Conversely, germanium is an efficient photodiode material for both visible and infrared wavelengths due its high absorption coefficient.

Improved structures including multiple photodiodes and methods of fabricating a structure including multiple photodiodes are needed.

SUMMARY

In an embodiment of the invention, a structure includes a substrate having a first trench extending to a first depth into the substrate and a second trench extending to a second depth into the substrate that is greater than the first depth. A first photodiode includes a first light-absorbing layer comprised of a first material positioned in the first trench. A second photodiode includes a second light-absorbing layer comprised of a second material positioned in the second trench. The first material and the second material each comprise germanium.

In an embodiment of the invention, a method includes forming a first trench extending to a first depth into a substrate and a second trench extending to a second depth into the substrate that is greater than the first depth, forming a first photodiode including a first light-absorbing layer comprised of a first material positioned in the first trench, and forming a second photodiode including a second light-absorbing layer comprised of a second material positioned in the second trench. The first material and the second material each comprise germanium.

