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The effects of TiO 2 / Al 2 O 3 / MgF 2 triple-layer (TL) antireflection (AR) coating on reducing optical loss of GaInP/InGaAs/Ge triple-junction (TJ) solar cell have been investigated by using Essential Macleod Program software and Crosslight Apsys software, and compared to that of TiO 2 / Al 2 O 3 dual-layer (DL) AR coating. The DLAR and TLAR coatings have reduced the average optical reflectivity values of the TJ solar cells by around 18.9% and 22.2%, respectively. The conversion efficiency of TJ solar cell was increased by 21.29% and 29.44% with DLAR and TLAR coatings. External quantum efficiency values of TJ solar cells with DL and TLAR coating increased in full wavelength region due to the increase of photo generated current density caused by the reduction of surface reflectivity. Both simulation and experimental results showed that the TiO 2 / Al 2 O 3 / MgF 2 TLAR coating has better anti-reflecting properties over TiO 2 / Al 2 O 3 DLAR coating, and improved the overall performance of TJ solar cell more.

Minimizing the impact of radiation-induced degradation in dilute nitride based optoelectronic devices is crucial in its applications. The effects of 1-MeV electron irradiation (of 1 × 1014–1 × 1016 e/cm2 range) on undoped GaInNAs|GaAs single quantum-well (QW) structure has been studied by low-temperature photoluminescence (PL). PL spectra of GaInNAs|GaAs QW are measured before and after electron irradiation. The results show a slight enhancement of the PL intensity in relatively low electron fluence, and then subsequent deterioration of PL with the increase of cumulative electron fluences. The enhancement in PL intensity at low electron doses is explained by recombination-enhanced defect reaction model, and the degradation at high electron doses is explained by irradiation-induced defects in the lattice.

Alkali doping can suppress deleterious antisite defects in kesterite Cu2ZnSnS4 (CZTS) and improve the open-circuit voltage. In this study, the effects of light Na-doping on the performance and the band alignment of CZTS/CdS thin-film solar cells were investigated. CZTS:Na thin films were fabricated by the spin coating with 10% Na doping on the surface of CZTS. The Na-doping led to the narrower FWHM and larger grain size. The hole concentration and the conductivity were improved due to the NaZn shallow acceptor defects. In addition, Na-doping can improve the band alignment of absorber/buffer interface and inhibit SRH recombination by the Na passivation effect and the suppression of SnZn defects. The typical cliff-like conduction band offset (CBO) was reduced from 0.25 eV in CZTS:Na/CdS to 0.1 eV in CZTS/CdS heterojunction. CZTS:Na device exhibited a higher Voc of 653 mV than that of CZTS/CdS device. The maximum conversion efficiency reached 7.46%, increased by 44% after Na-doping. These results clarify the effect of Na-doping on the band structure of the heterojunction in CZTS solar cells and support a new aspect that synthesis of a surface-doping CZTS:Na absorber has great potential for future research.

In this work, the (Ag,Cu)2ZnSnS4 (ACZTS) thin films were fabricated via sputtering with a multi-target to form different layer stacks, i.e., (S1) ZnS/Sn/Cu/Ag/Mo,(S2) ZnS/Sn/Ag/Cu/Mo and (S3) ZnS/Ag/Sn/Cu/Mo. The stacked precursors were sulfurized through a soft annealing, followed by a two-step sulfurization in a chamber filled with N2 at standard atmospheric pressure. The x-ray photoelectron spectroscopy elemental profile showed a vertical non-uniform distribution of Ag in the film. Based on the results of scanning electron microscopy and electron probe microanalysis, Ag enrichment of the upper surface was beneficial for the grain size. Moreover, a dense, uniform surface could be obtained and the stability of the elemental composition could be maintained. After optimizing the order of the Ag layers, the efficiency of the solar cells increased from 1.30% to 3.65%, an improvement of 181%. The open circuit voltage is increased from 448 mV to 630 mV because of the reduced voids, increased grain size, and reduced CuZn antisite defects.

A 25 nm thick Ag thin film was sputtered between the Cu2ZnSnS4 (CZTS) absorber and Mo electrode to improve the back contact in CZTS solar cells. The CZTS absorber was fabricated via a cost-effective N,N-dimethylformamide-based solution method. X-ray diffraction and Raman spectroscopy demonstrated that Ag diffused into the CZTS and partially substituted Cu, which resulted in an increased lattice constant a and grain size. Ag doping of CZTS (ACZTS) reduced both the Sn-loss and the presence of voids. An ACZTS photovoltaic device (ITO/i-ZnO/CdS/ACZTS/Mo) was fabricated and showed higher EQE than the CZTS device over the wavelength range of 450–800 nm. The open circuit voltage increased (Voc) from 543 to 631 mV, the short circuit current density (Jsc) increased from 10.36 to 14.37 mA, and the efficiency increased from 2.02 to 3.43% after sputtering the Ag layer. This is mainly because Ag functions as a temporary protective layer that made a tighter combination between Mo and the CZTS absorber.

Electron irradiation causes atomic displacement damage and produces point defects in semiconductor materials. The formation and variation of defects determine the optical properties of semiconductors during the irradiation process. In this paper, Te-doped GaSb was irradiated by 1 MeV electrons, with fluence of 1 × 1015 electrons cm−2, and its optical properties investigated by temperature-dependent photoluminescence (PL) before and after irradiation. After irradiation, the peak position had a blue-shift and intensity was significantly enhanced. The carrier concentration increased from 4.14 × 1017 to 7.82 × 1017 cm−3 but mobility decreased from 2690 to 1780 cm2 V−1 s−1. These phenomena could be explained by the complex mechanism of defect decomposition, that is, the VGaGaSbTeSb defect decomposed into two independent VGaGaSb and TeSb defects. To verify this mechanism, undoped GaSb was irradiated under the same conditions and PL results indicated that electron irradiation had little effect on optical properties of undoped GaSb.

The epitaxy properties of GaAs-based GaSb thin films were investigated under different growth conditions to identify suitable smooth areas on GaSb epilayer surface for growing high-quality AlInSb metamorphic buffers. The results showed notable reduction in threading dislocation densities (TDDs) and hillocks densities (HDs) of GaSb buffer layer when the temperature of substrates rising to Tc (surface reconstruction conversion temperature) + 110 °C and growth rate decreasing to 0.25 mono layer per second (ML/s). These conditions led to gradual changes in GaSb epilayer surface morphologies from tiny hillocks to near-parallel steps. The AlInSb/GaSb compound buffers were studied by employing five different structures of AlInSb metamorphic buffer layers grown on optimized GaSb layers, and then analyzed by various analytical methods. The influence of various structural buffer layers on defects were evaluated in order to suppress the formation of defects. It was shown that the buffer layer with low-temperature interface layer and superlattice structure presents obvious inhibitory effects on defects. Among these, specimens with superlattice interface exhibits the lowest TDDs of 3.1 × 107 cm−2 and moderate HDs of 2.4 × 107 cm−2.

The electrical parameters and external quantum efficiency (EQE) of 3 MeV and 8 MeV proton beam irradiated upright metamorphic (UMM) GaInP/GaInAs/Ge triple-junction solar cells, grown by metal-organic chemical vapor deposition, have been investigated and compared to lattice-matched (LM) GaInP/GaInAs/Ge solar cells. High-resolution X-ray diffraction was used to study the relaxation of strain by analysing reciprocal space maps. Threading dislocation density was estimated from cathodoluminescence image. SRIM simulation results have been applied for analysing the irradiation induced displacement damage and its effects on cell performance. The results show that the electrical parameters of both UMM and LM cells degraded more by 3 MeV proton compared to 8 MeV proton irradiation. The degradation of V-oc and I-sc depends on each other in both UMM and LM cells but have different features under proton irradiation due to different cell configurations, materials, and parameters etc. EQE spectra of UMM and LM cells mainly degrades in longer wavelength region due to the reduction of minority carrier diffusion length. Top GaInP subcell in UMM cell shows better radiation resistance than LM cell due to the higher In-P composition, and middle GaInAs middle subcell in UMM structure shows weaker radiation resistance because of the relatively higher indium composition.

ZAO (ZnO: Al)/Al and ITO/Ag complex back-reflectors were successfully applied to substrate nip and superstrate pin amorphous silicon solar cells respectively. As a result, the short circuit current (Isc) for a cell with a complex back-reflector increases significantly as compared with a cell without a complex back-reflector. For a superstrate pin cell prepared on SnO2 coated glass, the short-circuit current even increases up to 30%.

The CdS film is one of the best candidates for the n-type buffer layer in Cu2ZnSnS4 (CZTS) solar cells. However, the inappropriate band alignment at CdS/CZTS heterojunction result in the high barrier for the photogenerated carriers, which decrease the open-circuit voltage and the short-circuit current. In this paper, the crystallization and the optical bandgap of the Zn-doping Cd0.6Zn0.4S film fabricated by chemical bath deposition were studied. XRD showed that the lattice constant of hexagonal Cd0.6Zn0.4S decreased a little after Zn doping because of the shorter bond length of Zn–S. Photoluminescence and transmittance spectra showed the band gap of Cd0.6Zn0.4S thin film increased from 2.59 to 2.88 eV due to Burstein-Moss shift. The conduction band offset (CBO) obviously decreased from 0.51 eV in CZTS/CdS heterojunction to 0.27 eV in CZTS/Cd0.6Zn0.4S heterojunction which result in the short-circuit current increasing from 12.25 to 15.05 mA/cm2. The conversion efficiency (Eff) and fill factor (FF) of the solar cell based on CZTS/Cd0.6Zn0.4S were increased from 2.31% to 31.06 to 4.88% and 47.45, comparing to CZTS/CdS solar cell.

In this study, a high performance TiO 2 / Al 2 O 3 / MgF 2 multilayer anti-reflective (AR) coating, with an average reflectivity of 6.36% in spectral range of 300–1800 nm, applied on GaInP/GaAs/Ge triple-junction solar cell was designed by Essential Macleod Program (EMP) software. Based on the simulation results, TiO 2 , Al 2 O 3 , MgF 2 single layer and TiO 2 / Al 2 O 3 / MgF 2 multilayer AR coating samples were grown by Electron Beam Evaporation (EBE) system for 1 MeV electron beam irradiation experiment. The overall reflectivity of TiO 2 / Al 2 O 3 / MgF 2 multilayer AR coating is decreased with the increase of electron irradiation fluence due to the change of reflectivity of each AR layer caused by the refractive index changes. This result indicates that the TiO 2 / Al 2 O 3 / MgF 2 multilayer AR coating can improve the triple junction solar cell radiation resistance by achieving favorable permeability in the broadband solar spectrum, especially in 750–900 nm region where the main degradation spectral window for triple junction solar cell.

1 meV electron irradiation and post thermal annealing effects of GaInAsN bulk material with bandgap energy of 1 eV was studied by low-temperature photoluminescence (PL). The nitrogen proportion of the samples was confirmed by high-resolution X-ray diffraction measurement as 0.26%. The result shows that the PL intensity and high activation energy non-radiative centers of GaInAsN materials degraded seriously due to the irradiation induced large number of defects. The PL enhancement phenomena were observed in all samples after rapid thermal annealing (RTA) at 650 ∘C for five minutes. The irradiation and RTA caused PL peak red-shift and blue-shift have been discussed.

In this account, a series of InAsSb thin films were grown on GaAs substrates with GaSb as buffer layer by MBE, the effect of nucleation layer grown under different conditions on the quality of InAsSb thin films was studied, and the inhibition effect of AlSb/GaSb superlattice structure (SLS) on defect propagation in heteroepitaxy was evaluated. In this process, the corresponding Sb/As BEP flux ratio changes of As/In BEP flux ratio are studied. The sensitivity of Sb/As BEP flux ratio to As beam change is eliminated by using locked As beam value and Sb/As BEP flux ratio, which improves the repeatability of epitaxial material component control. At the same time, the Sb content of the GaSb/InAsSb interface could be accurately tuned by controlling the opening sequence and time of the sources cell shutter. Released the increase of strain at the interface caused by too large Sb component. It can be used to control the composition of InAsSb materials.

The degradation characteristics of MOCVD grown InGaAsP/InGaAs dual junction solar cells, irradiated by 1 MeV electron, 3 MeV and 10 MeV proton, have been investigated. Main electrical and optical properties of solar cell degraded seriously with the increase of irradiation fluences due to the irradiation induced defects which are acting as non-radiative recombination centers in the active layers of the solar cell. The remaining factor of P m a x is 0.67, 0.53 and 0.51 for 1 MeV electron, 10 MeV proton, and 3 MeV proton irradiation, respectively, when the displacement damage dose (DDD) is 3 . 16 × 1 0 10 MeV/g. The degradation of external quantum efficiency (EQE) of each subcell mainly occurred in the long wavelength region, the integrated current density J s c of InGaAsP and InGaAs subcells degraded more seriously upon 3 MeV and 10 MeV proton irradiation comparing to 1 MeV electron irradiation. The InGaAsP subcell turned out to be the current limiting unit due to the lower J s c before and post irradiation. By applying equivalent displacement damage dose model, the relative damage coefficient for 3 MeV proton to 10 MeV proton and 1 MeV electron to 10 MeV proton have been calculated.

Low-temperature (T = 30 K) photoluminescence (PL) and post thermal annealing effects on 150 KeV proton irradiated GaInAsN bulk, single quantum well and triple quantum well structures (Eg ~ 1.0 eV) have been investigated. The nitrogen proportion of the samples was confirmed by high-resolution X-ray diffraction (HR-XRD) measurement as 0.26%, 0.30% and 0.20% for GaInAsN bulk, SQW, and MQW samples, respectively. The result shows that the PL intensity of GaInAsN materials degraded seriously by proton irradiation. The PL intensity enhancement were observed for all three types of sample after thermal annealing at 650 °C for 5 min, and MQW sample was recovered by the factor bigger than 100. The irradiation induced red-shift and thermal annealing induced blue-shift phenomena were analyzed by SRIM simulation result and theoretical models of InGaAs band structure.

We investigate the effects of 1.0MeV electron beam irradiation on the photoluminescence of self-assembled InAs/GaAs quantum dots. After irradiation doses up to 1×1016e-/cm2 , photoluminescence of all samples was degraded dramatically and some additional radiation-induced changes in photo-carrier recombination from QDs, which include a slight increase in PL emission with low electron doses under different photo-injection condition in two samples, are also noticed. Different energy shift was observed in two samples with different Quantum Dot sizes. We attribute this remarkable phenomenon to combination of stress relaxation induced red-shift and In-Ga intermixing caused blue-shift.

The electrical parameters and EQE spectral response of 1 MeV electron beam irradiated MOVPE grown lattice-matched (LM) and upright metamorphic (UMM) GaInP/GaInAs/Ge triple-junction solar cells have been investigated with different flux density and fluence range from $5\times 10^{14}$ to $1.5\times 10^{15}\mathbf{cm}^{-2}$ . The overall degradation of electrical parameters of UMM cell was higher than LM cell due to the existence of dislocation within the epitaxy active layers. It was observed that the EQE spectra degrade mainly in top and middle subcells, and top GaInP subcell in UMM cell showed better radiation resistance due to the higher InP composition. An artifact phenomenon was observed in bottom Ge subcell due to the low shunt resistance.

Properties and passivation effect of ultra-thin AlN films fabricated on InGaAs/GaAs near-surface quantum wells by plasma-enhanced atomic layer deposition are investigated. The role of the coating on the surface is studied by examining the electric field build-up by photoreflectance. Photoluminescence confirms the passivation effect with ultra-thin layers and the reduced electric fields with thicker AlN layers. Atomic force microscopy shows that an ultra-thin AlN layer does not substantially alter the surface morphology.

In this paper we reported the electrical and spectral properties of 1 MeV electron and 3 MeV proton irradiated In0.53Ga0.47As single junction solar cell, which is used as the fourth subcell of wafer bonded GaInP/GaAs//InGaAsP/InGaAs four-junction full spectra solar cell. The equivalent displacement damage dose model was applied to study the radiation effects of solar cell. The results show that the electrical parameters of the solar cell degrade seriously with the increase of irradiation fluences, the reduction of minority carrier life-time and changes of series and shunt resistance caused by irradiation-induced displacement damage are the main reason for the degradation of cell performance. Degradation of spectral response mainly occurred in the long wavelength region of solar cell due to the bigger displacement damage in the base layer of solar cell. Degradation properties of solar cell by electron and proton irradiation can be predicted by electron to proton damage equivalency factor Rep.

The effects of electron beam and gamma-ray irradiation on the optical properties of InGaAs/GaAs quantum dot (QD), quantum well (QW), and bulk structures, which were grown by metal organic vapor phase epitaxy, have been investigated. Optical properties of all the structures were degraded by both kinds of irradiation. Electron beam irradiation caused a larger reduction in the photoluminescence (PL) intensity and carrier lifetime of the samples than gamma-ray irradiation. Also, red-shift of the PL peak was observed in almost all the irradiated QD and QW structures. Comparing the different structures, the QD structure showed the best radiation resistance.

The changes in output parameters of 1 MeV electron irradiated MOCVD grown upright metamorphic (UMM) GaInP/GaInAs/Ge triple junction solar cells have been studied. Non-ionizing energy loss (NIEL) approach and MULASSIS simulation were applied for analyzing the effects of irradiation induced displacement damage on cell performance. The influence of base thickness on radiation resistance has been studied by changing the base thickness of top GaInP and middle GaInAs subcell, respectively. The experimental results show that the electrical parameters, Voc, Isc, and Pmax of UMM cell degrade with the increase of electron fluence. The change of spectra response indicates middle GaInAs subcell degrades more severe than top GaInP subcells, and the base thickness of two subcells has different effects on spectra response of UMM cell.

A low-temperature passivation method for GaAs surfaces is investigated. Ultrathin AlN layers are deposited by plasma-enhanced atomic-layer-deposition at 200 ° C on top of near-surface InGaAs/GaAs quantum well structures. A significant passivation effect is seen as shown by up to 30 times higher photoluminescence intensity and up to seven times longer lifetime compared to uncoated reference samples. The improved optical properties are accompanied by a redshift of the quantum well photoluminescence peak likely caused by a combination of the nitridation of the GaAs capping layer and a surface coupling effect.

Transformation of InAs islands into quantum rings (QRs) by metal organic vapor phase epitaxy is investigated by using a GaAs partial capping layer followed by annealing under tertiarybutylarsine (TBAs) flow. QRs with the density of 10 7 – 10 9 cm - 2 are obtained at 500 – 600 ∘ C . The optimum values for the annealing time and the partial capping layer thickness are found to be 60–120 s and 0.5–2.0 nm, respectively. Both a thicker cap layer and shorter annealing time produce an obvious suppression of the ring evolution. The geometric shape of the rings is elongated in [1 1 0] direction due to the anisotropy of the diffusion rate of the indium atoms. However, this elongation is reduced in the QRs annealed at higher temperatures. Low-temperature (10 K) photoluminescence (PL) peak at 1.22 eV with the full width at half maximum of about 80 meV is obtained from the buried QRs grown at 550 ∘ C . A blue shift of the PL peak is observed when the annealing temperature is increased. This energy shift is probably due to the changes in the ring size and in the indium composition of the ring.

The suitability of titanium nitride (TiN) for GaAs surface passivation and protection is investigated. A 2–6-nm thick TiN passivation layer is deposited by atomic layer deposition (ALD) at 275 ° C on top of InGaAs/GaAs near surface quantum well (NSQW) structures to study the surface passivation. X-ray reflectivity measurements are used to determine the physical properties of the passivation layer. TiN passivation does not affect the surface morphology of the samples, but increases significantly the photoluminescence intensity and carrier lifetime of the NSQWs, and also provides long-term protection of the sample surface. This study shows that ALD TiN coating is a promising low-temperature method for ex situ GaAs surface passivation.

The growth and surface passivation of near-surface InGaAs quantum wells (QWs) on GaAs (1 1 0) substrate have been investigated. Triangular shaped small islands, approximate areal density of 10 7 cm � 2 , are observed on metal organic vapor phase epitaxially grown GaAs single layer and InGaAs multi-quantum wells (MQWs) surfaces in a wide range of growth temperatures. By optimizing the growth conditions, high quality In0:22Ga0:78As QWs with optical properties comparable to the same structure grown on GaAs (1 0 0) are obtained. Near-surface single QWs are used to study the surface passivation. Epitaxially in situ grown mono-layer thick GaP and InP layers as well as surface phosphorization with tertiarybutylphosphine (TBP) are utilized as passivation methods. Passivation significantly increases photoluminescence (PL) intensity and carrier lifetime of near-surface QWs. The best passivation efficiency is obtained by surface phosphorization with TBP on (1 1 0)-oriented near-surface QW while the ultra-thin InP layer is the best on (1 0 0)-oriented nearsurface QW. After 7 months of air exposure, all passivated near-surface QWs still show high PL intensity comparable to deep QW while the PL intensity of unpassivated samples degraded severely. Also, the differences between the optical properties of QWs on GaAs (1 1 0) and (1 0 0) substrates are observed and discussed.

The GaAs surface passivation effects of epitaxially grown ultra-thin GaP layers and surface As–P exchange have been investigated. Optical properties of passivated and unpassivated InGaAs/GaAs near-surface quantum wells (QWs) grown by metal organic vapor phase epitaxy (MOVPE) are studied by low-temperature continuous-wave and time-resolved photoluminescence (PL). By optimizing the growth conditions, smooth surface morphologies and significant improvement of optical properties were observed for both passivation methods. Passivation improved the PL intensity more than two orders of magnitude and notably increased the PL decay time.

The carrier dynamics in strain-induced InGaAsP/InP quantum dots (QDs) is investigated by time-resolved photoluminescence and continuous-wave photoluminescence. The stressor QDs are fabricated by depositing self-assembled InAs islands (or stressor islands) on top of a near-surface InGaAsP/InP quantum well (QW). The temporal behaviour of the QD photoluminescence transients are observed to exhibit a two-phase decay. Rate equation analyses reveal that by increasing the distance of the QW from the surface the surface capture time constant is increased considerably while the capture time constant of an electron from the QW to the QD is decreased.

Although conventional III-V compound semiconductors are often considered not to exhibit an efficiency droop, a pronounced low temperature droop was recently measured in AlGaInP/GaAs multi-quantum well structures. In this work, we investigate the efficiency droop in simple optically pumped lattice matched InGaAs/InP single well heterostructures to exclude charge transport related effects from the measurements. The results show that droop is present in this very simplistic setup and, furthermore, starts approximately at the same carrier density as in typical III-N structures. Our results suggest that in its most fundamental form, droop can be explained by Auger-like processes.

Demonstrating and harnessing electroluminescent cooling at technologically viable cooling powers requires the ability to routinely fabricate large area high quality light-emitting diodes (LEDs). Detailed information on the performance and yield of relevant large area devices is not available, however. Here, we report extensive information on the yield and related large area scaling of InP/InGaAs LEDs and discuss the origin of the failure mechanisms based on lock-in thermographic imaging. The studied LEDs were fabricated as mesa structures of various sizes on epistructures grown at five different facilities specialized in the growth of III-V compound semiconductors. While the smaller mesas generally showed relatively good electrical characteristics and low leakage current densities, some of them also exhibited unusually large leakage current densities. The provided information is critical for the development and design of the optical cooling technologies relying on large area devices.

The transformation of InAs islands to quantum rings (QRs) by metalorganic vapor phase epitaxy is investigated. After covering the InAs islands with a thin GaAs partial capping layer and annealing under tertiarybutylarsine (TBAs) flow, ring-shaped nanostructures with a density of 10(7)-10(9) cm(-2) are obtained at 500-600 °C. The effects of the growth temperature, annealing process and thickness of the partial capping layer are studied. Optimum values for the annealing time and the partial capping layer thickness were found to be 60-120 s and 0.5-2.0 nm, respectively. Low temperature photoluminescence (PL) emission peaks from islands and QRs grown at 500 °C are observed at 1.04 eV and 1.22 eV, respectively. The annealing temperature affected the QR evolution and the PL emission from the QRs due to the temperature dependence of the diffusion rate of indium atoms.

The optical properties of the in situ epitaxial GaN and InP passivated InGaAs∕GaAs near-surface quantum wells, which were fabricated by metal organic vapor phase epitaxy, are investigated. Low-temperature photoluminescence (PL), time-resolved photoluminescence, and photoreflectance are used to study the passivation effect. Both GaN and InP passivations are observed to significantly enhance the PL intensity and carrier lifetime and to reduce the surface electrical fields. Comparison of the methods shows that the epitaxial InP passivation is more effective. However, epitaxial GaN and nitridation methods are comparable with InP passivation.