Room Temperature Direct Band Gap Emission from Ge p-i-n Heterojunction Photodiodes

Abstract

Room temperature direct band gap emission is observed for Si-substrate-based Ge p-i-n heterojunction photodiode structures operated under forward bias. Comparisons of electroluminescence with photoluminescence spectra allow separating emission from intrinsic Ge (0.8 eV) and highly doped Ge (0.73 eV). Electroluminescence stems from carrier injection into the intrinsic layer, whereas photoluminescence originates from the highly n-doped top layer because the exciting visible laser wavelength is strongly absorbed in Ge. High doping levels led to an apparent band gap narrowing from carrier-impurity interaction. The emission shifts to higher wavelengths with increasing current level which is explained by device heating. The heterostructure layer sequence and the light emitting device are similar to earlier presented photodetectors. This is an important aspect for monolithic integration of silicon microelectronics and silicon photonics.

Electroluminescence of highly doped Ge pnn diodes for Si integrated lasers

“…Furthermore, an increase in strain can be ruled out from XRD measurements. Compared to previous results reported in pin [6,11] and pnn [7] heterostructures, we present the first clear evidence of a red band gap shift in Ge light emitting devices created by heating effects. The emission intensity of the diode increases superlinearly with respect to voltage owing to an indirect valley filling effect which scatters more electrons to the direct valley under injection.…”

Electroluminescence of germanium LEDs on silicon: Influence of antimony doping

“…It can be attributed to the highly doped contact area as this peak was already found around 0.73 eV in photoluminescence (PL) investigations [6]. It could be possible that the effect of charge carrier penetrating the oppositely doped regions is stronger when applying The intensity of the n + region is significantly increased leading to a changed shape of the spectrum to a wider peak broadening.…”

“…The shift of the Fermi level to higher energies caused by high n-type doping and the modification of the band structure by tensile straining of the Ge layer. Proof of this concept was already done by different groups [3][4][5][6].…”

Extended Defect Propagation in Highly Tensile-Strained Ge Waveguides

“…Many approaches to inducing tensile strain for Ge lasers and more efficient light emitters have been demonstrated [11][12][13][14][15][16][17][18][19]. The first optically pumped Ge laser used 0.15% biaxial strain plus degenerate n-type doping to partly populate the Γ valley with electrons despite the indirect bandgap [2].…”

“…Enhanced electroluminescence from Ge light-emitting diodes (LEDs) has been demonstrated based on tensile-strained Ge with different stressors, but power efficiency needs to be significantly improved for practical lasers [13][14][15][16]. Enhanced direct-bandgap photoluminescence has similarly been demonstrated [20][21][22].…”