Impact of growth conditions on the spatial non‐uniformities of composition in InGaP epitaxial layers

Gregušová, D.; Kučera, M.; Hasenöhrl, S.; Vávra, I.; Strichovanec, Pavel; Martaus, J.; Novák, J.

doi:10.1002/pssc.200674131

Cited by 3 publications

(1 citation statement)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The luminescent signal was filtered using a quarter-meter monochromator and was detected by a silicon photodiode using a standard lock-in technique. The layer composition was calculated from the PL peak position after [8] using the expression E g (x) = 2.549 − 1.347x.…”

Section: Methodsmentioning

confidence: 99%

Epitaxial Growth of GaP/InxGa1-xP (xIn ≥ 0.27) Virtual Substrate for Optoelectronic Applications

Hasenöhrl¹,

Novák²,

Vávra³

et al. 2011

Journal of Electrical Engineering

View full text Add to dashboard Cite

Compositionally graded epitaxial semiconductor buffer layers are prepared with the aim of using them as a virtual substrate for following growth of heterostructures with the lattice parameter different from that of the substrates available on market (GaAs, GaP, InP or InAs). In this paper we report on the preparation of the step graded InxGa 1−x P buffer layers on the GaP substrate. The final InxGa 1−x P composition x In was chosen to be at least 0.27 . At this composition the InxGa 1−x P band-gap structure converts from the indirect to the direct one and the material of such composition is suitable for application in light emitting diode structures. Our task was to design a set of layers with graded composition (graded buffer layer) and to optimize growth parameters with the aim to prepare strain relaxed template of quality suitable for the subsequent epitaxial growth.K e y w o r d s: crystal structure, organometallic vapor phase epitaxy (OMVPE), semiconducting III-V materials INTRODUCTIONThe excellent properties of blue light emitting diodes (LEDs) based on nitride semiconductor compounds enabled the subsequent developments in solid state lighting. The red side of the visible spectrum is successfully covered with high brightness LED diodes based on (Al x Ga 1−x ) 0.5 In 0.5 P material lattice matched to GaAs. The low efficiency of green sources (so called "green or yellow gap") that are necessary for white and full color applications remains still a problem which has to be solved.One way how to do it is to use InGaN LEDs emitting blue light which is converted down by suitable color converter-phosphor. Such sources can be used for producing white light but they can also emit nearly monochromatic, high-color-purity light [1].Green light LED sources can be also realized on a base of (Al x Ga 1−x ) 0.5 In 0.5 P material lattice matched to GaAs and joined to the optically transparent GaP substrate by wafer bonding technique [2]. For green emission the content of Al has to be higher than 0.3. Increasing the Al content leads to significant decrease in internal radiative recombination efficiency and causes problems with p-type doping [3].Another approach is to prepare the light emitting structure in Al free In x Ga 1−x P ternary alloy deposited directly on GaP substrate. The In x Ga 1−x P alloy exhibits the direct band gap structure (energy gap of 2.24 eV, emission at 554 nm) for the indium content higher than 0.27. The disadvantage of this method is that the lattice parameter of In 0.27 Ga 0.73 P is about a 2.1 % higher than that of GaP substrate. It is necessary to insert between the substrate and the active region an intermediate layer enabling the change of the lattice constant from the substrate to the final active layer. Very important function of this layer is to be able to filter the dislocation propagation to the electroluminescent part of the structure. What is convenient, such graded buffer will be optically transparent for light emitted from LED because of decreasing band-gap with increasing indium content...

show abstract

Section: Methodsmentioning

confidence: 99%

Epitaxial Growth of GaP/InxGa1-xP (xIn ≥ 0.27) Virtual Substrate for Optoelectronic Applications

Hasenöhrl¹,

Novák²,

Vávra³

et al. 2011

Journal of Electrical Engineering

View full text Add to dashboard Cite

show abstract

Metamorphic GaAsP buffers for growth of wide-bandgap InGaP solar cells

Simon

Tomasulo

Simmonds

et al. 2011

Journal of Applied Physics

View full text Add to dashboard Cite

GaAs x P 1 − x graded buffers were grown via solid source molecular beam epitaxy (MBE) to enable the fabrication of wide-bandgap InyGa1−yP solar cells. Tensile-strained GaAsxP1−x buffers grown on GaAs using unoptimized conditions exhibited asymmetric strain relaxation along with formation of faceted trenches, 100–300 nm deep, running parallel to the [01¯1] direction. We engineered a 6 μm thick grading structure to minimize the faceted trench density and achieve symmetric strain relaxation while maintaining a threading dislocation density of ≤106 cm−2. In comparison, compressively-strained graded GaAsxP1−x buffers on GaP showed nearly-complete strain relaxation of the top layers and no evidence of trenches but possessed threading dislocation densities that were one order of magnitude higher. We subsequently grew and fabricated wide-bandgap InyGa1−yP solar cells on our GaAsxP1−x buffers. Transmission electron microscopy measurements gave no indication of CuPt ordering. We obtained open circuit voltage as high as 1.42 V for In0.39Ga0.61P with a bandgap of 2.0 eV. Our results indicate MBE-grown InyGa1−yP is a promising material for the top junction of a future multijunction solar cell.

show abstract