Structural and Optical Behavior of Germanium Quantum Dots

Abstract

Controlled growth, synthesis, and characterization of a high density and large-scale Ge nanostructure by an easy fabrication method are key issues for optoelectronic devices. Ge quantum dots (QDs) having a density of ∼10 11 cm −2 and a size as small as ∼8 nm are grown by radio frequency magnetron sputtering on Si (100) substrates under different heat treatments. The annealing temperature dependent structural and optical properties are measured using AFM, XRD, FESEM, EDX, photoluminescence (PL) and Raman spectroscopy. The effect of annealing is found to coarsen the Ge QDs from pyramidal to dome-shaped structures as they grow larger and transform the nanoislands into relatively stable and steady state configurations. Consequently, the annealing allows the intermixing of Si into the Ge QDs and thereby reduces the strain energy that enhances the formation of larger nanoislands. The room temperature PL spectra exhibits two strong peaks at ∼2.87 eV and ∼3.21 eV attributed to the interaction between Ge, GeO𝑥 and the possibility of the presence of QDs core-shell structure.No reports so far exist on the red shift ∼0.05 eV of the strongest PL peak that results from the effect of quantum confinement. Furthermore, the Raman spectra for the pre-annealed QDs that consist of three peaks at around ∼305.25 cm −1 , 409.19 cm −1 and 515.25 cm −1 are attributed to Ge-Ge, Ge-Si, and Si-Si vibration modes, respectively. The Ge-Ge optical phonon frequency shift (∼3.27 cm −1 ) associated with the annealed samples is assigned to the variation of shape, size distribution, and Ge composition in different QDs. The variation in the annealing dependent surface roughness and the number density is found to be in the range of ∼0.83 to ∼2.24 nm and ∼4.41 to ∼2.14 × 10 11 cm −2 , respectively.

Linear and nonlinear optical properties of functionalized CdSe quantum dots prepared by plasma sputtering and wet chemistry

“…The growth mechanisms will be discussed in detail as a function of the RFMS parameters in a forthcoming paper where it will be shown that the QDs adopt dome-shaped structures similar to the ones reported by Samavati et al for germanium quantum dots [18] as depicted in Fig. S1.…”

“…Controlling the sputtering parameters, such as the pressure in the vacuum chamber, also allows the tuning of the NPs size and therefore of their optical properties [13]. RFMS was previously successfully used for the deposition of TiO 2 , Ge, Si, ZnO, GaAs, CuInSe 2 and CdS QDs [13][14][15][16][17][18][19][20][21][22]. RFMS was also applied to the deposition of CdSe thin film and CdSe quantum dots embedded in SiO 2 or in an organic matrix [23,24].…”

Formation of Uniform Germanium Islands on Silicon Substrate Using Nickel as Catalyst by Thermal Evaporation Method

“…Several methods are employed to fabricate GIs with dierent sizes, such as chemical vapor deposition [1,2], radio frequency magnetron sputtering [3,4], molecular beam epitaxy [57], and thermal evaporation [8]. However, establishing a method to achieve suciently uniform island sizes with regular spatial distribution remains a critical issue.…”

Germanium nanoislands grown by radio frequency magnetron sputtering: Annealing time dependent surface morphology and photoluminescence

“…Understanding the growth of Ge nanoislands using the Stranski-Krastanov mechanism is topically important and fundamentally challenging for device functionality. [1] Transforming an indirect band gap material (such as bulk Ge) to a direct gap material (nanosized Ge) gives rise to light emission, which is very attractive for full-color display as well as integrated optoelectronics technology. Among the techniques used to fabricate lowdimensional semiconductor structures, radio-frequency (rf) magnetron sputtering has several advantages, including low deposition temperature, higher film purity when compared to existing melting techniques, [2,3] easy fabrication, and low cost.…”