Germanium Semiconductor Substrate for LED Source Fabrication

In the past few decades, researchers have invested tremendous effort in expanding the application fields of silicon-based complementary metal oxide semiconductor CMOS electronic technology to integrated photonics. In particular, the monolithic integration of Group IV materials and their devices has attracted widespread attention, mainly due to their compatibility with CMOS processes. Although key photonic devices such as modulators, waveguides, and detectors have been successfully integrated into silicon-based electronic chips, the indirect bandgap characteristics of silicon limit the single chip integration of high-efficiency light sources on its chips. In contrast, germanium, as a multi valley indirect bandgap semiconductor material, possesses both direct and indirect interband radiation recombination, and has a more suitable band structure for direct bandgap inversion. Germanium (Ge) has been used to demonstrate high-performance photodetectors, modulators, waveguides, and other optical components. Recently, there has been a significant increase in interest in germanium semiconductor as a group IV laser source after demonstrating optical gain and laser generation through the use of optics and electrical injection. You can buy germanium single crystal substrate from PAM-XIAMEN for the manufacturing of LED light sources, with specific parameters as follows:

1. Germanium Semiconductor Substrate for Preparing LED Source

PAM240304 – GELED

Item	Prime Grade Ge Substrate
Diameter	100mm
Thickness	500um
Orientation	（100）
Doping	Intrinsic
Resistivity	10-50 ohm-cm
Surface finished	SSP/DSP

2. How to Enhance the Luminescence Efficiency of Germanium?

Although germanium has a direct bandgap of 0.8 eV, it is essentially an indirect bandgap material due to the presence of an L-conduction band located 0.136 eV below the ᴦ – conduction band valley, as shown in Fig. 1 (a). This energy difference makes germanium an inefficient light emitter, as most externally injected electrons will occupy the lower energy L conduction band valley. When the recombination rate of emitted photons is low, electrons located in the L conduction valley can only recombine with holes with the help of phonons. However, by filling the indirect L valley in the conduction band, we can observe direct recombination at point of ᴦ-. On the other hand, electrons located in the ᴦ- conduction valley can recombine with holes at a higher recombination rate. Therefore, by making germanium a direct or pseudo direct bandgap material, we can increase the carrier recombination rate from the ᴦ- combination valley and make germanium an energy-saving optical emitter.

Fig. 1 Band gap diagram of germanium: a) bulk germanium and b) Energy band engineering using tensile strain and n-type doped germanium. The tensile strain reduces the energy difference between the T and L valleys, while n-type doping compensates for the remaining energy difference. Strain can also cause splitting of light and heavy hole bands

According to reports, direct optical transitions in germanium are a very fast process, with a radiative recombination rate five orders of magnitude higher than indirect transitions. This means that the direct gap emission of germanium is as efficient as that of direct gap semiconductors. By utilizing the direct bandgap transition of germanium, the luminescence of germanium can be significantly enhanced. Usually, by introducing tensile strain, n-type doping, or alloys of Ge and tin, germanium can be transformed from a fundamentally indirect bandgap material to a direct bandgap material, as shown in Fig. 1 (b). Both methods reduce the bandgap in germanium, meaning that the bandgap at the direct valley decreases at a higher rate than the indirect L-valley. As a result, the bandgap structure of germanium in electronics is altered, ultimately transforming it into a direct bandgap material that can absorb or emit light.

As the tensile stress increases, the expected luminescence will be greater. In theory, it has been proven that germanium can be engineered through tensile stress and n-type doping to achieve better direct bandgap light emission at room temperature. The engineering of germanium semiconductor bandgap through tensile stress provides the possibility for the development of novel optoelectronic devices that are fully compatible with silicon technology, such as light-emitting diodes (LEDs), lasers, optical modulators, etc. Germanium semiconductor uses are from energy tunable light collectors (such as photodetectors) to efficient optoelectronic devices.

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