Page - 190 - in Photovoltaic Materials and Electronic Devices

Materials 2015, 8 4547 Figure 2. RHEED diffraction pattern. (a) During the growth of GaAs; (b) after the deposition of the InAs QDs. 2.2. Material Characterization Figure 3 illustrates the ω/2θ, reflection peaks of pin-GaAs/n+-Si with and without InAs/InGaAs multistaked QDs. Figure 3. The ω/2θ of reflection peak of: (a) pin-GaAs/ Si; (b) pin-GaAs/Si with InAs/InGaAs multilayer QDs. The spectra from the pin-GaAs (a) and pin-GaAs with QDs (b) grown on Si substrate reveal the presence of two peaks centered on θ = 34.52° and θ = 33.06° and attributed respectively to the silicon substrate and to the GaAs layer. Additionally, a third peak appear at θ = 32.75° in the XRD spectra of the structure containing the QDs. This peak can be attributed to the InAs/InGaAs multilayer with a nominal indium composition xm equal to the average of indium compositions in all layers (xm = 13.27% estimated by HRXRD). For the InAs/GaAs multistaked QDs grown on GaAs substrate, the HRXRD spectra show the appearance of other peaks appointed satellite peaks, due to the periodicity introduced by the bilayers repetition and the angular period of this peak is related to the thickness of the bilayer [28,29]. In our case, the absence of satellite peaks could be explained by the existence of defects produced in the interfaces layers. Indeed, as shown by the Figure 4, the cross Figure 2. RHEEDdiffractionpattern. (a) t growthofGaAs; (b) after he dep sitionof the InAsQDs. 2.2.MaterialCharacterization Figure 3 illustrates th ω/2θ, reflection pe k of pin-GaAs/n+-Si with a d without InAs/InGaAsmultistakedQDs. Materials 2015, 8 4547 Figure 2. RHE D diffraction pat er ring the growth of GaAs; (b) after the deposition of the InAs QD . 2.2. Material Char cterization Figure 3 illustrates the ω/2θ, reflection peaks of pin-GaAs/n+-Si with and without InAs/InGaAs multistaked QDs. Figure 3. The ω/2θ of reflection peak of: (a) pin-GaAs/ Si; (b) pin-GaAs/Si with InAs/InGaAs multilayer QDs. The spectra from the pin-GaAs (a) and pin-GaAs with QDs (b) grown on Si substrate reveal the presence of two peaks centered on θ = 34.52° and θ = 33.06° and attributed respectively to the silicon substrate and to the GaAs layer. Additionally, a third peak appear at θ = 32.75° in the XRD spectra of the structure containing the QDs. This peak can be attributed to the InAs/InGaAs multilayer with a nominal indium composition xm equal to the average of indium compositions in all layers (xm = 13.27% estimated by HRXRD). For the InAs/GaAs multistaked QDs grown on GaAs substrate, the HRXRD spectra show the appearance of other peaks appointed satellite peaks, due to the periodicity introduced by the bilayers repetition and the angular period of this peak is related to the thickness of the bilayer [28,29]. In our case, the absence of satellite peaks could be explained by the existence of defects produced in the interfaces layers. Indeed, as shown by the Figure 4, the cross Figure 3. Theω/2θofreflectionpeakof: (a)pin-GaAs/Si; (b)pin-GaAs/Siwith InAs/InGaAsmultilayerQDs. The spec ra from the pin-GaAs (a) and pin-GaAs with QDs (b) grown on Si substrate r veal the prese ce of two peaks centered onθ= 34.52˝ andθ= 33.06˝ and attributed respectively to the silicon substrate and to the GaAs layer. Additionally, a third peak appear atθ= 32.75˝ in the XRD spectra of the structure containing the QDs. This peak can be attributed to the InAs/InGaAs multilayer with a nominal indium composition xm equal to the average of indium compositions in all layers (xm = 13.27% estimated by HRXRD). For the InAs/GaAs multistaked QDs grown on 190