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Ptak, Aaron J. (ORCID:0000000309978964)

Publications and source records attributed to Ptak, Aaron J. (ORCID:0000000309978964).

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Toward High-Throughput Deposition of III-V Materials and Devices Using Halide Vapor Phase Epitaxy: Preprint

III-V devices are used in countless applications due to their excellent physical properties. They could become more prevalent, especially in area-intensive applications such as solar power, if they can achieve significant cost decreases through increasing scale. The development of high-throughput growth systems can help to achieve this scale, leading to the use of III-V devices in areas where they are not currently economically feasible. Here, we describe a pilot production, pseudo inline HVPE reactor with the potential to greatly increase the throughput of III-V devices. We show computational modeling results that both informed system design and the understanding of the impact of different process parameters on the deposition. We show the throughput possibilities of this reactor with an example solar cell device design but note that this system is agnostic to the device structure and can be used to increase the throughput of lasers, LEDs, transistors, and more III-V devices.

high throughput↗
DOE OSTI2023

Improving Performance of III-V Solar Cells Grown on Spalled Germanium with Ex Situ Substrate Planarization

Controlled spalling allows removal of devices and provides an opportunity for cost reduction through substrate reuse. However, the fracture-based process can leave behind morphological surface features, notably river lines, that can disrupt epitaxial growth and degrade device performance. We investigate the viability of various wet etch chemistries to planarize river lines to ensure high-quality device growth and performance without mechanical repolishing, and so maintain a route towards cost-effective reuse. Etching in a HF: HNO 3 :CH 3 COOH solution effectively planarizes river lines and produces a surface that yields devices with equivalent performance to those grown on epi-ready Ge wafer surfaces. Further studies will focus on optimizing etch composition, temperature, and time to minimize material removal while maintaining a suitable surface for high-quality epitaxy.

germanium↗
DOE OSTI2023

Development of HVPE-Grown III-V Solar Cells Passivated with AlInP

We present the first AlInP-passivated solar cells grown by dynamic hydride vapor phase epitaxy (D-HVPE). Single junction (1J) GaAs and GaInP/GaAs (2J) tandems with AlInP passivation achieve AM1.5G efficiencies of 26.0% and 28.5%, respectively, which are the highest reported efficiencies for HVPE-grown devices of each type. 1J devices passivated with either AlInP or GaInP exhibit similar VOC and long wavelength current collection, indicating that both windows provide similar passivation. Adding AlInP passivation to the 2J solar cell improves the VOC by -50 mV relative to the device passivated by a GaInP emitter. These achievements remove one of the last barriers limiting parity of HVPE device efficiencies with state-of-the-art.

AlInP↗
DOE OSTI2023

Morphology Control of Growth by Hydride Vapor Phase Epitaxy on Faceted GaAs Substrates Produced by Controlled Spalling for Low Cost III-V Devices

In this work, we apply the morphology control of hydride vapor phase epitaxial (HVPE) growth to planarize faceted, non-planar substrates. Controlled spalling is a promising high-throughput substrate reuse technology that could reduce substrate costs for III-V devices; however, the spalling fracture for (100)-oriented GaAs substrates produces a regularly corrugated surface of facets that are 5-20 um in height. We discuss how to planarize these surfaces using only a few minutes of HVPE growth and how to minimize the impact on throughput when integrating faceted wafers into a potential manufacturing process at scale.

epitaxy↗
DOE OSTI2022

GaAs Substrate Recycling Using in-situ Deposited NaCl Layers via Molecular Beam Epitaxy

This work presents an alternative method to conventional III-V substrate recycling methods via growth of NaCl on nearly-lattice matched GaAs (001) substrates. Reflection high energy electron diffraction and transmission electron microscopy confirm an epitaxial relationship between the NaCl layers and the underlying GaAs. If the sample is heated too much prior to GaAs deposition, the NaCl fully desorbs from the surface. The quality of the deposition of GaAs on NaCl ranges from amorphous at low temperature to polycrystalline at intermediate temperatures. Exposure to electron beams during growth results in larger and (001) textured grains. The substrate is separated from the GaAs film in seconds via submersion in water, revealing a substrate surface comparable to the original.

electron beams↗
DOE OSTI2022

Recent HVPE Grown Solar Cells at NREL: Preprint

In this work we present solar cells grown via hydride vapor phase epitaxy (HVPE) in NREL's dynamic HVPE reactor. We show single junction GaAs and GaInP solar cells with efficiencies as high as 25.5% and 15.2% respectively, and dual junction solar cells with an efficiency of 24.9%.

GaAs↗
DOE OSTI2021

Effect of Doping Density on the Performance of Metamorphic GaInAs Solar Cells Grown by Dynamic Hydride Vapor Phase Epitaxy

We study the effect of doping density on the performance of inverted metamorphic ~1 eV GaInAs solar cells grown by dynamic hydride vapor phase epitaxy. We find that the doping efficiency of Se in this material is extremely high, with 5x10 17 cm -3 being the lowest controlled value we could achieve with our present Se source. We compared rear heterojunction devices grown with intentional n-doping of 5x10 17 cm -3 and unintentional n-doping of 5x10 15 cm -3 . The intentionally doped sample exhibited an open circuit voltage ~80 mV higher than the unintentionally doped sample due to reduced dark current, and a bandgap voltage offset, or W OC , of 0.407 V. We believe that future doping optimization will improve carrier collection and W OC in these devices.

GaAs↗
DOE OSTI2021

(110)-Oriented GaAs Devices and Spalling as a Platform for Low-Cost III-V Photovoltaics

We demonstrate the growth of (110) GaAs solar cells by hydride vapor phase epitaxy (HVPE) as an advance towards a (110)-oriented device platform with substrate reuse via spalling. Controlled spalling offers a fracture-based path to substrate amortization, allowing device removal and substrate reuse, but the faceted surface generated in spalling of (100)-GaAs presents hurdles to direct regrowth of subsequent devices. Spalling of (110)-oriented substrates takes advantage of the natural (110) cleavage plane in zinc-blende III-V materials, eliminating this faceting. The vast majority of III-V epitaxy development is on (100)-oriented substrates, but epitaxy is not limited to this orientation. Here, we demonstrate (110)-based GaAs solar cells grown by HVPE with equivalent performance to devices grown on the more standard (100) orientation. We also demonstrate spalling of (110) oriented substrates, revealing surfaces with flat terraces separated by steps. These results provide preliminary evidence of a potentially low-cost path for terrestrial III-V photovoltaics via the (110) substrate orientation.

(110) orientation↗
DOE OSTI2021

Planarization of Rough (100) GaAs Substrates via Growth by Hydride Vapor Phase Epitaxy

Wafer reuse techniques help offset the cost of III-V growth substrates by using a single wafer for multiple growths, but costly re-polishing after device removal limits the end benefit. In this work, we present planarization growth by hydride vapor-phase epitaxy (HVPE), a potentially low-cost growth technique, as a method of smoothing rough substrates for subsequent high-quality device growth without the need for polishing. First, we show there is a threshold for allowable substrate roughness without device degradation by comparing devices grown by organometallic vapor-phase epitaxy (OMVPE) on epi-ready polished and pre-polished substrates that did not have the final epi-ready polish. We then demonstrate successful smoothing with HVPE growth on substrates with different surface morphologies, with features ranging from general roughness to large facets. Initial devices grown by HVPE on a pre-polished substate showed no degradation compared to a control wafer, indicating that planarizing rough substrates through HVPE growth is a promising path toward being able to use rough substrates directly for growth, without costly polishing steps.

GaAs↗
DOE OSTI2021

Facet Suppression in (100) GaAs Spalling via Use of a Nanoimprint Lithography Release Layer

Controlled spalling is an emerging technique developed for fast, scalable wafer reuse, but for the commonly used (100) GaAs substrate system, the process leaves large facets ranging from 5-10 µm on the wafer surface. Removing them for wafer reuse requires a costly re-polishing step that limits the cost savings that can be achieved with spalling as a wafer reuse technique. In this study, we investigate facet suppression in spalling of (100) GaAs by redirecting the fracture front along features created by buried nanoimprint lithography (NIL)-patterned SiO 2 . We show successful facet suppression using patterns that result in favorable fracture along the SiO 2 /GaAs interface. The results from this work show NIL patterned interlayers are a promising method for faceting suppression in (100) GaAs spalling.

controlled spalling↗
DOE OSTI2021

GaAs Solar Cells Grown on Intentionally-Contaminated GaAs Substrates

III-V solar cells have the best performance of any semiconductor materials, but deposition of these materials relies on high-quality single crystal GaAs wafers for their superior performance. Unfortunately, the cost of these wafers makes these high-efficiency devices only accessible in high-value or niche markets. Here, we explored the effect of growing bulk GaAs crystals with lower purity input materials in order to reduce their cost. We observe that intentional impurities added to the melt before the crystal growth occurs segregate to the top of the boule. Single junction GaAs solar cells grown on wafers made from contaminated boules showed no performance degradation compared to a high-purity control wafer. These results suggest that lower purity Ga and As source materials can be used during crystal growth to reduce the cost of wafers.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2021

Demonstration of Passivation Using a Low-Temperature-Grown, Al-Containing Window Layer by HVPE

We present hydride vapor phase epitaxy (HVPE) growth of single junction GaAs solar cells with Al0.4Ga0.6As front passivation layers at a growth temperature of 650°C. Devices achieved a short circuit current density of ~27.52 mA/cm2 after anti-reflection coating, similar to devices that used GaInP windows with the same bandgap, indicating that AlGaAs provides front-surface passivation resulting in a low interface recombination velocity. The low temperature growth of Al containing III-V materials by HVPE allows for compatibility with In-containing alloys in high-efficiency III-V device structures for various applications.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2021

Control of CuPt Ordering in GaInP Grown by Hydride Vapor Phase Epitaxy

We investigate the degree of ordering present in GaInP layers grown by dynamic hydride vapor phase epitaxy (D-HVPE) as a function of various growth conditions. We assess order parameter from both transmission electron and x-ray diffraction and compare these trends to the order parameter estimated by the photoluminescence-determined band gap in the GaInP layers. The degree of ordering increases with deposition temperature and the ratio of gas-phase group V to group III precursors in the reactor. We also investigate the effect of growth rate, demonstrating the capability of HVPE to suppress order through rapid growth rates. Such ordering dependences are consistent with mechanisms established for ordering observed in GaInP grown by organometallic vapor phase epitaxy (OMVPE), but with weaker ordering than GaInP grown by that method.

growth↗
DOE OSTI2021

Improved Contacts for Tandem Cells with Enhanced Effciency Grown by D-HVPE

Dynamic hydride vapor phase epitaxy (D-HVPE) has provided a potential route towards lower cost material growth of III-V photovoltaic devices. A highly doped Ga0.5In0.5P emitter layer is grown in attempt to force passivation at the front of the cell to account for the absence of a suitable window layer in our reactor. Control over dopant diffusion in these materials is thus critical to achieving high-efficiency device performance. Here, we institute a two-step contact layer design that boosts tandem cell efficiencies by minimizing Se diffusion into the underlying emitter layer while still providing sufficiently low contact resistance. Short-circuit current in these devices improves to 8.9 mA/cm2 in an uncoated GaInP/GaAs cell, an improvement of 1.2 mA/cm2 over our previous best cell. Conversion efficiency with the new contact doping scheme is projected to be ~27% with the inclusion of a standard ARC layer.

27 ARPA - Advanced Research Projects Agency-Energy↗