Characterization of the manufacturing processes to grow triple-junction solar cells

A number of important but little-investigated problems connected with III-V/Ge heterostructure in the GaInP/GaInAs/Ge multijunction solar cells grown by MOVPE are considered in the paper. The opportunity for successfully applying the combination of reflectance and reflectance anisotropy spectroscopy in situ methods for investigating III-V structure growth on a Ge substrate has been demonstrated. Photovoltaic properties of the III-V/Ge narrow-band subcell of the triple-junction solar cells have been investigated. It has been shown that there are excess currents in the Ge photovoltaic p-n junctions, and they have the tunneling or thermotunneling character. The values of the diode parameters for these current flow mechanisms have been determined. The potential barrier at the III-V/Ge interface was determined and the origin of this barrier formation during MOVPE heterogrowth was suggested

Monolithic and hybrid integration of InAs/GaAs quantum dot microdisk lasers on silicon

A method of hybrid integration of quantum dot microdisk lasers with silicon wafer is proposed and realized. In addition to the possibility of combining microlasers with various silicon-based electronic and photonic devices, this makes it possible to significantly improve heat removal from the active region of the microlaser. The thermal resistance normalized to the mesa area reaches the level of about 0.002 (K/W)*cm2, which is significantly lower than the corresponding values of QD microlasers on GaAs substrate and monolithically grown on Si. As a result, the threshold current as well as current-induced shift of emission wavelength are reduced in continuous-wave regime

Increasing the quantum efficiency of InAs/GaAs QD arrays for solar cells grown by MOVPE without using strain-balance technology

Research into the formation of InAs quantum dots (QDs) in GaAs using the metalorganic vapor phase epitaxy technique ispresented. This technique is deemed to be cheaper than the more often used and studied molecular beam epitaxy. The bestconditions for obtaining a high photoluminescence response, indicating a good material quality, have been found among awide range of possibilities. Solar cells with an excellent quantum ef?ciency have been obtained, with a sub-bandgapphoto-response of 0.07 mA/cm2per QD layer, the highest achieved so far with the InAs/GaAs system, proving the potentialof this technology to be able to increase the ef?ciency of lattice-matched multi-junction solar cells and contributing to abetter understanding of QD technology toward the achievement of practical intermediate-band solar cells

Lasing of InP/AlInAs quantum dots in AlInAs microdisk cavity

AlInAs microdisk cavities having quality factor Q ~ 15 000 were fabricated from lattice-matched InP/AlInAs (interface/aggregation) quantum dot (QD) structures using wet chemical etching. The QD emission coupled to whispering gallery modes was observed at spectral range 920 - 1000 nm at temperatures of 10 - 160 K. The laser generation with threshold power density of 50 W/cm2 at T = 10 K was observed under optical pumping. It was found that the spontaneous emission coupling factor β equals 0.23 for these microdisks. The low temperature lasing operation and the small coupling factors observed suggest the existence of small QDs formed at the InP/InAlAs interface as the main active elements

Atomic ordering and bond relaxation in optical spectra of self-organized InP/GaInP2 Wigner molecule structures

A.M.M., D.V.L., and A.S.V. acknowledge the support of the Russian Science Foundation Grant No. 19-19-00246. K.G.B., M.V.R., and A.A.T. acknowledge the financial support of the Russian Foundation for Basic Research (Project No. 18-02-01212). This research was also enabled by the Science Foundation Ireland under Grant Nos. 15/IA/2864, 12/RC/2276, 12/RC/2276-P2, and 18/US/3512, and the Northern Ireland Department for the Economy (Grant No. USI-140). A.B.N. acknowledges support from EPSRC grant no. EP/R023751/1.We used transmission electron microscopy, Raman, and photoluminescence spectroscopy to identify the effect of CuPt-type GaP-InP atomic ordering (AO) on the structural and emission properties of self-organized (SO) InP/GaInP2 Wigner molecule (WM) quantum dot (QD) structures. We found that the correlation of AO and SO growth results in the formation of InP/GaInP2 QD/AO-domain (QD/AOD) core-shell composites. This observation shows that intrinsic WMs in this system emerge due to a strong piezoelectric field generated by AODs, which induces QD doping and a built-in magnetic field. We found that the bond relaxation of AODs leads to a decrease in the emission energy of WMs of 80 meV. The photoluminescence spectra of single WMs having an emission energy ∼1.53 eV are presented here, the lowest one reported for this system.Publisher PDFPeer reviewe

Impact of N on the atomic-scale Sb distribution in quaternary GaAsSbN-capped InAs quantum dots

The use of GaAsSbN capping layers on InAs/GaAs quantum dots (QDs) has recently been proposed for micro- and optoelectronic applications for their ability to independently tailor electron and hole confinement potentials. However, there is a lack of knowledge about the structural and compositional changes associated with the process of simultaneous Sb and N incorporation. In the present work, we have characterized using transmission electron microscopy techniques the effects of adding N in the GaAsSb/InAs/GaAs QD system. Firstly, strain maps of the regions away from the InAs QDs had revealed a huge reduction of the strain fields with the N incorporation but a higher inhomogeneity, which points to a composition modulation enhancement with the presence of Sb-rich and Sb-poor regions in the range of a few nanometers. On the other hand, the average strain in the QDs and surroundings is also similar in both cases. It could be explained by the accumulation of Sb above the QDs, compensating the tensile strain induced by the N incorporation together with an In-Ga intermixing inhibition. Indeed, compositional maps of column resolution from aberration-corrected Z-contrast images confirmed that the addition of N enhances the preferential deposition of Sb above the InAs QD, giving rise to an undulation of the growth front. As an outcome, the strong redshift in the photoluminescence spectrum of the GaAsSbN sample cannot be attributed only to the N-related reduction of the conduction band offset but also to an enhancement of the effect of Sb on the QD band structure

Near field scanning optical microscopy for investigation of high power semiconductor lasers

В данной работе были исследованы карты распределения ближнего поля InGaAs/GaAs/AlGaAs полосковых инжекционных лазеров при различных токах накачки. Было показано, что в структурах, состоящих из двух резонансно связанных волноводов, наблюдается подавление мод высоких порядков.Near field intensity distributions of InGaAs/GaAs/AlGaAs lasers including broadened waveguides based on coupled large optical cavity (CLOC) structures were investigated. It was demonstrated that scanning near field optical microscopy gives direct proof of suppressing the transverse high-order mode lasing.Работа выполнена при поддержке РНФ (соглашение № 14-42-00006-П