Growth of InGaAs Solar Cells on InP(001) Miscut Substrates Using Solid‐Source Molecular Beam Epitaxy

Abstract

Herein, the effects of both the growth temperature and the substrate miscut on the properties of lattice‐matched InGaAs solar cells grown on InP substrates via solid‐source molecular beam epitaxy are investigated. The growth temperature is varied from 420 to 490 °C. InP(001) miscut by 2° toward (111)A and (111)B denoted by 2°A and 2°B, respectively, and exactly‐cut substrates are used. Material quality is evaluated by photoluminescence (PL) and atomic force microscopy (AFM) measurements. At room temperature, the PL emissions become more intense at higher growth temperatures and with miscut substrates, indicating less nonradiative recombination. AFM results show a streaky surface with step structures along the [11¯0 ] direction for cell grown at 490 °C on 2°A, suggesting that the substrate promotes step‐flow growth. Consequently, the highest conversion efficiency (12.3%) for the cell grown at 490 °C on 2°A is obtained. Especially, the open‐circuit voltage (VOC) increases from the baseline of 0.350 V (for the cell grown at 420 °C on an exact substrate) to 0.374 V. The Eg−VOC deficit, where Woc=Enormalg/q−Voc, of 369 mV is obtained, which is a standard benchmark for high‐material‐quality solar cells.

Simulation of 0.67 eV-InGaAs solar cell with InP window-layers of various thickness on virtual InP/AlGaInAs/GaAs substrates

“…For instance, the 3-junction lattice mismatched solar cell can be extended to a 4-junction or more junction on GaAs substrate by adding another lattice mismatched Ga x In 1−x As junction. The In x Ga 1−x As heteroepitaxial growth on GaAs substrate has been applied to many terrestrial and space energy conversion applications for the following reasons: (i) the ternary In x Ga 1−x As semiconductor with varied bandgap energy from 0.36 to 1.42 eV is suitable for the most optic-electronic devices [8], such as thermophotovoltaic [9], III-V semiconductor solar cells [10] and lasers [11]; (ii) the carries mobility of In x Ga 1−x As material is high, which can be applied in high speed electronic devices [12]. Recently, A metamorphic Al 0.18 Ga 0.33 In 0.49 P/Al 0.23 Ga 0.77 As/Ga-As/Ga 0.66 In 0.34 As/Ga 0.42 In 0.58 As 6-junction solar cell by NREL [13] have demonstrated AM1.5 143-suns efficiencies in exceed of 47.1%, The 6-J solar cell is proposed to match the solar spectrum and balance the photocurrent generated from each subcell, of which Ga 0.66 In 0.34 As and Ga 0.42 In 0.58 As subcells are lattice-mismatched to GaAs substrate.…”

Inhomogeneous in-plane distribution of preferential glide planes of β dislocations in a metamorphic InGaAs solar cell

“…We also calculated the bandgap-voltage offset, W oc (=E g /q − V oc ), 5,19,20) of the cell used in this study and obtained 0.454 V. For latticematched 0.74 eV InGaAs solar cells, lower W oc values of 0.34 and 0.369 V have been reported. 19,20) Lattice-mismatched InGaAs solar cells have shown voltage losses of about 0.38 V compared to their bandgap energies and in these devices threading dislocation densities were about 2 × 10 6 cm −2 . 5) These W oc values are below 0.4 V, which is the range of values achieved by solar cells with a high material quality solar cell.…”

Nondestructive characterization of threading dislocations in graded buffer layers of inverted metamorphic solar cells by two-photon excitation spectroscopy

“…From the I-V curves of these samples, we found that the bandgap-voltage offset W oc (=E g /q − V oc ) 34,35) values for samples A and B are 0.585 V and 0.438 V, respectively. The W oc value reflects the crystal quality of a junction, and high-quality IMM1J InGaAs solar cells have a W oc below 0.4 V. 35) Therefore, sample A has a significantly poorer crystal quality than the high-quality devices reported previously.…”