Room Temperature Photoluminescence of Intrinsic and Doped Bulk Germanium Using Additional Excitation Source

Date of Award


Degree Name

M.S. in Electro-Optics


Department of Electro-Optics and Photonics


Jay Mathews


Over the past 50 years, silicon (Si) based complementary metal oxide semiconductors have been fundamental within the electronics industry. The stable oxide, silicon dioxide, as well as the abundance of Si, has allowed for the growth of a multi-billion-dollar industry. The demand for Si electronics is high, but increasing interest lies in photonic-integrated circuits. If a proper light source could be achieved on Si it would revolutionize the photonics industry. Signal processing speed could be increased by orders of magnitude resulting in greater bandwidth in signal transmission. However, the limitations of Si prevent it from being used as an efficient light source. Germanium (Ge) is an indirect band gap semiconductor, but the minima of the conduction band at the L and Γ points differ by only 140meV at room temperature. This results in significant luminescence from the direct band gap; thus, it is often referred to as a quasi-direct band gap material. The direct gap luminescence can be used to create optical gain, and further enhancement in luminescence can be achieved through doping. In 2012, these ideas were used to create an electrically pumped Ge diode laser. However, the device suffered from poor efficiency. Understanding the luminescence properties of Ge while under high-injection conditions produced through external excitation, similar to what the material in a laser diode would experience, could lead to new device designs and improvements in efficiency. In this research, photoluminescence (PL) from bulk doped and intrinsic Ge wafers were studied under different excitation conditions. The samples were excited with a 980nm, low power, probe laser source and two high powered CW pumps to observe the effects on the PL. The spontaneous emission was collected and dispersed using a grating spectrometer (0.13NA, 140mm focal length, 300 lines/mm) with a 77K cooled extended InGaAs. The PL shows an increase in the Γ bandgap luminescence relative to the indirect bandgap luminescence at high doping concentrations and increased excitation. Using a 1908nm pump source, additional peaks were observed in the luminescence spectra for all three doped samples. These could be attributed to transitions between the conduction/valence bands and trap states within the bandgap. The results indicate that bulk Ge that has been Czochralski (CZ) grown likely contains a significant number of point defects.


Physics, Solid State Physics, Optics

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