Nanophotonic circuits using group III-nitrides on silicon are still lacking one key component: efficient electrical injection. In this paper we demonstrate an electrical injection scheme using a ...metal microbridge contact in thin III-nitride on silicon mushroom-type microrings that is compatible with integrated nanophotonic circuits with the goal of achieving electrically injected lasing. Using a central buried n-contact to bypass the insulating buffer layers, we are able to underetch the microring, which is essential for maintaining vertical confinement in a thin disk. We demonstrate direct current room-temperature electroluminescence with 440 mW/cm
output power density at 20 mA from such microrings with diameters of 30 to 50 μm. The first steps towards achieving an integrated photonic circuit are demonstrated.
Strain engineering is a powerful approach in micro- and optoelectronics to enhance carrier mobility, tune the bandgap of heterostructures, or break lattice symmetry for nonlinear optics. The ...dielectric stressors and bonding interfaces used for strain engineering in photonics can however limit thermal dissipation and the maximum operation temperature of devices. We demonstrate a new approach for enhanced thermal dissipation with stressor layers by combining metals and dielectrics. The method is applied to the germanium semiconductor. All-around tensile-strained germanium microdisks have been fabricated with metallic pedestals. The transferred tensile strain leads to a germanium thin film with a direct bandgap. Under continuous wave optical pumping, the emission of the whispering gallery modes is characterized by a threshold and an abrupt linewidth narrowing by a factor larger than 2. The occurrence of stimulated emission is corroborated by modeling of the optical gain. This demonstrates lasing with pure germanium microdisks.
We propose to use Ge-dielectric-metal stacking to allow one to address both thermal management with the metal as an efficient heat sink and tensile strain engineering with the buried dielectric as a ...stressor layer. This scheme is particularly useful for the development of Ge-based optical sources. We demonstrate experimentally the relevance of this approach by comparing the optical response of tensile-strained Ge microdisks with an Al heat sink or an oxide pedestal. Photoluminescence indicates a much reduced temperature rise in the microdisk (16 K with Al pedestal against 200 K with SiO
pedestal under a 9 mW continuous wave optical pumping). An excellent agreement is found with finite element modeling of the temperature rise. This original stacking combining metal and dielectrics is promising for integrated photonics where thermal management is an issue.
Silicon (Si), germanium (Ge) and Si1−xGex alloys are currently used as active layers in microprocessors. Si and Ge are fully miscible and their interdiffusion can occur even at room temperature. ...Thus, well-controlled Ge/Si interdiffusion is crucial to insure the performance of electronic devices. During the course of our experiments to synthesize tensile-strained and n-doped Ge/Si films for optoelectronic applications, we notice that Ge/Si interdiffusion could affect the optical properties of Ge/Si films. We report here an approach to use carbon (C) adsorption on Ge to minimize Ge/Si interdiffusion. Since carbon atoms have a small atomic radius, deposited carbon can occupy vacancies and interstitial sites in Ge. This allows to greatly reduce Ge/Si interdiffusion because diffusion mechanisms via vacancies and interstitial sites are known to have the lowest activation energy. In addition, by optimizing the deposited C amount, one can maintain the epitaxial growth process of Ge/Si heterostructures.
Ge emerges as a good candidate for the active layer in optoelectronic devices and is compatible with complementary metal oxide semiconductor technology. As the Ge band structure exhibits an indirect ...band gap with a small difference in energy between the direct and the indirect valleys (about 140 meV), the energy band structure can be modified by applying a tensile strain or by doping electrons into the film to turn Ge into a semiconductor material with a direct ban gap structure. In this work, Ge epilayers were grown on Si substrate by molecular beam epitaxy technique, and we show that the tensile strain value of the Ge epilayers increases by a factor of two by doping electrons into the films with two donor elements using GaP and Sb sources. The dopant concentration in Ge epilayers is 5.6 × 10
19
at cm
−3
for the P dopant and 6.4 × 10
18
at cm
−3
for the Sb dopant. The activated electron concentration was found to be up to 4.10
19
cm
−3
in the Ge film. A gain of photoluminescence (PL) intensity three times higher than the sample doped only with P atoms was obtained. This result contributes to the perspective that Ge films can be utilized in functional optoelectronic as well as photonic devices.
We have combined numerous characterization techniques to investigate the growth of tensile-strained and n-doped Ge films on Si(001) substrates by means of solid-source molecular-beam epitaxy. The Ge ...growth was carried out using a two-step growth method: a low-temperature growth to produce strain relaxed and smooth buffer layers, followed by a high-temperature growth to get high crystalline quality Ge layers. It is shown that the Ge/Si Stranski–Krastanov growth mode can be completely suppressed when the growth is performed at substrate temperatures ranging between 260°C and 300°C. X-ray diffraction measurements indicate that the Ge films grown at temperatures of 700–770°C are tensile-strained with typical values lying in the range of 0.22–0.24%. Cyclic annealing allows further increase in the tensile strain up to 0.30%, which represents the highest value ever reported in the Ge/Si system. n-Doping of Ge was carried out using a GaP decomposition source. It is shown that heavy n-doping levels are obtained at low substrate temperatures (210–250°C). For a GaP source temperature of 725°C and a substrate temperature of 210°C, a phosphorus concentration of about 1019cm−3 can be obtained. Photoluminescence measurements reveal an intensity enhancement of about 16 times of the direct band gap emission and display a redshift of 25meV that can be attributed to band gap narrowing due to a high n-doping level. Finally, we discuss about growth strategies allowing optimizing the Ge growth/doping process for optoelectronic applications.
•We investigate the effect of tensile strain and n-doping on Ge optical properties.•We show that cyclic annealing allows getting a tensile strain up to 0.30% in Ge.•n-Doping of Ge/Si films is performed using a GaP decomposition source.•We show that n-doping is more important to enhance the photoluminescence intensity.•We present new growth strategies to develop Ge-based optoelectronic devices.
We report room temperature electroluminescence of tensile-strained germanium microdisks. The strain is transferred into the microdisks using silicon nitride stressors. Carrier injection is achieved ...with Schottky contacts on n-type doped germanium. We show that a biaxial tensile-strain up to 0.72% can be transferred by optimizing the carrier injection profile. The transferred strain is measured by the electroluminescence spectral red-shift and compared to finite element modeling. We discuss the impact of this strain level to achieve population inversion in germanium.
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