Low Background Doping Research Articles

(Invited) Vertical GaN Devices for High-Power Electronics

With the demand of high-power and high-speed electronics, GaN has achieved widespread interest owing to its wide-bandgap (WBG), large breakdown field, and high mobility that can provide superior performance compared to the Si and SiC that are limited by inherent material properties. In power electronics, GaN is a potential candidate due to its high-quality p-n junctions and availability of native substrates to prevent dislocation-assisted leakage, particularly for vertical devices. For high-power electronics, these vertical devices are more advantageous compared to their lateral counterparts due to their high current capability from large-area backside ohmic, high breakdown voltage from confined electric field within WBG material, scaling feasibility, and better thermal management. Moreover, the punch-through vertical device can extract the full potential of the WBG semiconductors by maximizing the average electric field over the fully depleted drift layer.For high-performance vertical device, high-quality drift layers with low controlled background doping and low compensating defects are essential to obtain the expected high breakdown voltage and low on-resistance. Hence, we have focused on both materials and device development for GaN power devices. Toward the first goal of high-quality GaN epitaxy, we optimized the growth condition for controlled low unintentionally doped (UID) and low impurity drift layer from ammonia molecular beam epitaxy (NH3 MBE). For this, we performed a systematic study of growth rate effects on the drift layer doping for a series of growth rates from 0.37 µm/hr to 1.68 µm/hr in both sapphire and free-standing GaN substrates (Fig. 1). A low background UID doping of ~1015 cm-3 was achieved with a growth rate 1.4 µm/hr on the free-standing GaN substrate. This UID background doping is one of the lowest reported for GaN homoepitaxy [1-3]. The potential of NH3 MBE-growth for low-doped epitaxy is recognized from our work, contributed from the cleaner growth environment of MBE, compared to the conventional metal-organic chemical vapor deposition (MOCVD).The next step of our work involved developing high-performance power devices with these high-quality epitaxies. Our vertical p-n GaN diode consisted of a ~4 µm UID GaN drift layer on ~0.25 µm of n+ GaN ([Si]: 1×1019 cm-3) buffer for the n-type region. The p-type region included a 10 nm p++ GaN cap ([Mg]: 3×1020 cm-3) to support the anode ohmic contact followed by a 0.4 µm p+GaN ([Mg]: 3×1019 cm-3) to form the p-n junction.The sample was fabricated with circular diodes of 80-100 µm diameter Pd/Pt Anode and a backside Ti/ Au Cathode. The field management was achieved by a combination of ~1.4 µm dry etch mesa isolation with a sidewall angle of ~55° and field plate (Fig. 2). For the field-plate dielectric, a stack of atomic layer deposition of Al2O3 (26 nm) and plasma-enhanced chemical vapor deposition of Si3N4 (205 nm) at 300 °C was used. Finally, a Ti/Pt metal stack of 15 µm length was patterned to form the field-plate.Capacitance-Voltage characteristics performed in these p-n diodes showed a doping of ~3×1015 cm-3 in the n- drift layer (Fig. 3a). Secondary ion mass spectrometry (SIMS) detected Si~2×1015 cm-3 and O ~2×1016 cm-3 respectively across the n-layer (Fig. 3b), likely the source of UID doping, accounting for their possible partial ionization. The compensating carbon impurities was less than the SIMS detection limit, certifying the high-quality NH3 MBE-growth. The forward J-V characteristics (Fig. 4) revealed the leakage current below the detection limit (~1.6 pA) for V<2 V. At higher forward biases (V=2.87 V) in the diffusion current region, the ideality factor reaches to a minimum of 1.36. The extracted specific on-resistance (Ron,sp) of 0.28 mΩ-cm2 and the minimum ideality factor of 1.36 are among the best achieved in vertical homoepitaxy GaN p-n diodes [1-3]. The highest breakdown voltage of these diodes were > 1 kV (equipment limit 1 kV) whereas some diodes exhibited breakdown at -890 V (Fig. 5). Silvaco simulation showed a punch-through breakdown of the diodes with peak electric field (EC) >2.6 MV/cm. Remarkably, this breakdown performance with NH3 MBE GaN of only ~4 um channel is comparable with the best available MOCVD GaN p-n diodes with a significantly thicker drift layer of ≥ 8 um (Fig. 6). Our work thus demonstrates the potential of high-performance power devices by NH3 MBE, benefitted from high-quality epitaxy, controlled low doping, and fast growth rates, that will be promising for high-voltage devices.

Impact of growth parameters on the background doping of GaN films grown by ammonia and plasma-assisted molecular beam epitaxy for high-voltage vertical power switches

We report on ammonia and plasma-assisted molecular beam epitaxy (NH3-MBE and PAMBE) grown GaN layers with a low net carrier concentration (Nnet). Growth parameters, such as growth rate, V–III ratio, and plasma power, were investigated on different substrates to study their impact on surface morphology and background doping levels using atomic force microscopy and capacitance–voltage (C–V) measurements, respectively. The elevated growth rates are especially interesting for vertical power switches, requiring very thick drift regions (over 10 μm) with low background concentrations. For our NH3-MBE-grown layers, Nnet shows an almost linear increase with the growth rate. Using a freestanding substrate and at a fast growth rate of 1.4 μm hr−1, a Nnet value as low as 1 × 1015 cm−3 was achieved. For samples grown via PAMBE, the lowest Nnet among samples grown under a Ga adlayer was 2 × 1016 cm−3 for a growth rate of 0.32 μm h−1 on a GaN-on-sapphire template. The results support the use of MBE for growing high-quality GaN material with reasonably fast growth rates maintaining low background doping levels for high-voltage vertical power electronic devices.

Mid-infrared interference coatings with excess optical loss below 10 ppm.

We present high-reflectivity substrate-transferred single-crystal GaAs/AlGaAs interference coatings at a center wavelength of 4.54 μm with record-low excess optical loss below 10 parts per million. These high-performance mirrors are realized via a novel microfabrication process that differs significantly from the production of amorphous multilayers generated via physical vapor deposition processes. This new process enables reduced scatter loss due to the low surface and interfacial roughness, while low background doping in epitaxial growth ensures strongly reduced absorption. We report on a suite of optical measurements, including cavity ring-down, transmittance spectroscopy, and direct absorption tests to reveal the optical losses for a set of prototype mirrors. In the course of these measurements, we observe a unique polarization-orientation-dependent loss mechanism which we attribute to elastic anisotropy of these strained epitaxial multilayers. A future increase in layer count and a corresponding reduction of transmittance will enable optical resonators with a finesse in excess of 100 000 in the mid-infrared spectral region, allowing for advances in high resolution spectroscopy, narrow-linewidth laser stabilization, and ultrasensitive measurements of various light-matter interactions.

Over 1 kV Vertical GaN-on-GaN p-n Diodes With Low On-Resistance Using Ammonia Molecular Beam Epitaxy

Vertical GaN-on-GaN p-n diodes grown by ammonia molecular beam epitaxy (NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> MBE) are reported in this letter for prospective high-power application devices. The diodes, consisting of only 4 μm drift layer with low unintentionalbackgrounddoping of ~ 3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , showed a maximum breakdown voltage of >1.0 kV and a low differential specific on-resistance of 0.28 mΩ-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Moreover, these diodes exhibited an excellent rectifying behavior with a low minimum ideality factor of 1.36 and a punch-through electric field comparable to the state-of-the-art vertical GaN-on-GaN p-n diodes grown by metalorganic chemical vapor deposition (MOCVD). These results suggest that all-MBE vertical GaN-on-GaN p-n diodes grown by NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> MBE can be promising for small-size high-power electronic devices.

(Invited) GaN Homoepitaxial Growth and Substrate-Dependent Effects for Vertical Power Devices

Vertical GaN power switch technology is expected to be utilized in next-generation medium to high voltage power converters due to the low ON-resistance and high breakdown voltage enabled by the improved critical electric field and mobility compared to Si and SiC-based devices. As large area substrates have become available by hydride vapor phase epitaxy (HVPE) and ammonothermal growth, the properties of nitrides are no longer dominated by defects introduced by heteroepitaxial growth, allowing recent realization of several fundamental vertical power devices, including diodes with edge termination, trench MOSFETs, and CAVETs. However, additional materials challenges are coming to the forefront that need to be understood and surmounted in order to allow vertical GaN power devices to achieve their full potential, notably the realization of repeatable thick drift layers with low background doping. To enable this, a deeper understanding of substrate preparation and the effects of the substrate and growth initiation on the characteristics of the epitaxial layers is required for MOCVD growth of homoepitaxial films. We investigate these effects on epi morphology, uniformity, and impurity incorporation by growing simultaneously on wafers from different vendors. The goal of this work is to detect and identify defects in GaN substrates with a series of quick, non-destructive, inexpensive techniques with capabilities of mapping whole wafers. We have characterized multiple substrates from over eight suppliers and the homoepitaxy grown on those substrates. All the substrates had nominally similar as-received specifications (resistivity, thickness, off-cut angle, bow, surface finish). The substrates were evaluated with a variety of techniques including Raman spectroscopy, photoluminescence, white light interferometry, and Nomarski imaging, enabling to detection of different concentrations of grain boundaries, sample impurities, point defects, v-shaped pits, polishing defects, crystal stress damage, and non-uniform insulating and conducive regions. The substrates can be characterized in two different categories: those with uniform characteristics, including carrier concentration, and those without. Comparing these results to those from homoepitaxial growth on the same wafers, the effects are both subtle and overt. Macroscopic surface morphology, which has shown a direct correlation to leakage current, copies and exaggerates that of the underlying substrate. Photoluminescence of the homoepitaxial surface along with Raman spectroscopy show that non-uniformities in the substrate carrier concentration can continue into the epitaxy. Following optical characterization, vertical Schottky diodes were fabricated to quickly evaluate device performance. While most of the films showed the ability to withstand high electric fields, those with more uniform properties in the substrate also showed more uniform electrical properties. These results show that the bulk substrates enable the path to high voltage vertical devices, but also show the significant influence that substrates can play in device performance.

Low background doping in AlInN grown on GaN via metalorganic vapor phase epitaxy

Nearly lattice-matched and unintentionally doped AlInN films with low background doping grown via metalorganic vapor phase epitaxy on GaN/sapphire are investigated. The lattice-matched condition is verified with x-ray diffraction (XRD), and the films exhibit typical morphological characteristics for AlInN. The optical constants (nr &k) and thicknesses of the AlInN films are determined via spectroscopic ellipsometry, finding an nr ~ 2.2 at 500 nm and a bandgap of ~4.366 eV. Temperature-dependent Hall measurements in the Van der Pauw configuration are performed for temperatures from 80 K up to 350 K, and a low background doping concentration (n ~ 3 × 1017 cm−3) and high electron mobility (μe ~ 320 cm2/V∙s) are found at room temperature. Simulations are performed to determine the influence of the 2-D electron gas (2DEG) caused by polarization fields from the GaN/AlInN interface and validate the Hall measurements. Thus, this work shows the potential of achieving high-quality AlInN films with low background doping densities for use in power electronic devices and deep-ultraviolet light-emitting diodes.

(Invited) Homoepitaxial GaN Growth and Substrate-Dependent Effects

Vertical GaN power switch technology is expected to be utilized in next-generation medium to high voltage power converters due to the low ON-resistance and high breakdown voltage enabled by the improved critical electric field and mobility compared to Si and SiC-based devices. As large area substrates have become available by hydride vapor phase epitaxy (HVPE) and ammonothermal growth, the properties of nitrides are no longer dominated by defects introduced by heteroepitaxial growth, allowing recent realization of several fundamental vertical power devices, including diodes with edge termination, trench MOSFETs, and CAVETs. However, additional materials challenges are coming to the forefront that need to be understood and surmounted in order to allow vertical GaN power devices to achieve their full potential, notably the realization of repeatable thick drift layers with low background doping. To enable this, a deeper understanding of substrate preparation and the effects of the substrate and growth initiation on the characteristics of the epitaxial layers is required for MOCVD growth of homoepitaxial films. We investigate these effects on epi morphology, uniformity, and impurity incorporation by growing simultaneously on wafers from different vendors. The goal of this work is to detect and identify defects in GaN substrates with a series of quick, non-destructive, inexpensive techniques with capabilities of mapping whole wafers. Four different substrates - three grown by hydride vapor phase epitaxy and the fourth by ammonothermal technique were obtained from multiple vendors. All had nominally similar as-received specifications (resistivity, thickness, off-cut angle, bow, surface finish). The substrates were evaluated with a variety of techniques including Raman spectroscopy, photoluminescence, white light interferometry, and Nomarski imaging, enabling to detection of different concentrations of grain boundaries, sample impurities, point defects, v-shaped pits, polishing defects, crystal stress damage, and non-uniform insulating and conducive regions. Comparing these results to those from homoepitaxial growth on the same wafers, the effects are both subtle and overt. Macroscopic surface morphology, which has shown a direct correlation to leakage current, copies and exaggerates that of the underlying substrate. Donor incorporation in the epitaxy is relatively uniform, regardless of the substrate doping. However, homoepitaxy on substrates with inhomogeneous impurity incorporation did show some near band edge broadening by PL. Carbon incorporation varied with substrate offcut angle, which is supported by DFT calculations. All interfaces between epitaxy and substrate have a large Si peak, which requires further study. Following optical characterization, vertical Schottky diodes were fabricated to quickly evaluate device performance. While most of the films showed the ability to withstand high electric fields, those with more uniform properties in the substrate also showed more uniform electrical properties. These results show that the bulk substrates enable the path to high voltage vertical devices, but also show the significant influence that substrates can play in device performance.

Defect properties of InGaAsN layers grown as sub-monolayer digital alloys by molecular beam epitaxy

The defect properties of InGaAsN dilute nitrides grown as sub-monolayer digital alloys (SDAs) by molecular beam epitaxy for photovoltaic application were studied by space charge capacitance spectroscopy. Alloys of i-InGaAsN (Eg = 1.03 eV) were lattice-matched grown on GaAs wafers as a superlattice of InAs/GaAsN with one monolayer of InAs (&amp;lt;0.5 nm) between wide GaAsN (7–12 nm) layers as active layers in single-junction solar cells. Low p-type background doping was demonstrated at room temperature in samples with InGaAsN layers 900 nm and 1200 nm thick (less 1 × 1015 cm−3). According to admittance spectroscopy and deep-level transient spectroscopy measurements, the SDA approach leads to defect-free growth up to a thickness of 900 nm. An increase in thickness to 1200 nm leads to the formation of non-radiative recombination centers with an activation energy of 0.5 eV (NT = 8.4 × 1014 cm−3) and a shallow defect level at 0.20 eV. The last one leads to the appearance of additional doping, but its concentration is low (NT = 5 × 1014 cm−3) so it does not affect the photoelectric properties. However, further increase in thickness to 1600 nm, leads to significant growth of its concentration to (3–5) × 1015 cm−3, while the concentration of deep levels becomes 1.3 × 1015 cm−3. Therefore, additional free charge carriers appearing due to ionization of the shallow level change the band diagram from p-i-n to p-n junction at room temperature. It leads to a drop of the external quantum efficiency due to the effect of pulling electric field decrease in the p-n junction and an increased number of non-radiative recombination centers that negatively impact lifetimes in InGaAsN.

Photovoltaic characterisation of GaAsBi/GaAs multiple quantum well devices

A series of strained GaAsBi/GaAs multiple quantum well diodes are characterised to assess the potential of GaAsBi for photovoltaic applications. The devices are compared with strained and strain-balanced InGaAs based devices.The dark currents of the GaAsBi based devices are around 20 times higher than those of the InGaAs based devices. The GaAsBi devices that have undergone significant strain relaxation have dark currents that are a further 10–20 times higher.Quantum efficiency measurements show the GaAsBi devices have a lower energy absorption edge and stronger absorption than the strained InGaAs devices. These measurements also indicate incomplete carrier extraction from the GaAsBi based devices at short circuit, despite the devices having a relatively low background doping. This is attributed to hole trapping within the quantum wells, due to the large valence band offset of GaAsBi.

(Invited) Advances in SiC and GaN Power Device Development and Future Directions

As wide bandgap semiconductors, devices based on SiC and GaN represent critical next-generation medium voltage and high voltage power switch technology. SiC device technology has matured rapidly over the past two decades, owing to advances in substrate quality, a fundamental understanding of epitaxial growth to characterize defects and identify and eliminate performance-limiting defects such as basal plane dislocations, and device breakthroughs such as the junction barrier Schottky (JBS) diode and DMOSFET. While lateral GaN-based HEMT technology has been highly successful for RF power amplifiers and is well-positioned to supersede GaAs-based MMICs, advances in vertical power device technology has been limited due to the lack of high quality native substrates. As large area substrates have become available by hydride vapor phase epitaxy (HVPE) and ammonothermal growth, several fundamental vertical power devices have recently been realized, including Schottky diodes with edge termination, trench MOSFETs, and CAVETs. However, significant fundamental materials challenges currently limit device performance, specifically the realization of repeatable thick drift layers with low background doping as well as a reliable selective area planar process for p-type doping. In this presentation, an overview of SiC and GaN device development at the U.S. Naval Research Laboratory will be summarized, first looking at SiC devices including the development of novel materials characterization techniques to understand the role of defects on device performance, reliability and failure analysis of devices, including BPD kinetics in PiN and MPS diodes, and novel device designs including grayscale termination processes, temperature compensated PiN diodes, and hybrid Si/SiC modules. Recent developments in GaN vertical device technology will also be presented, including the development of an ion implanted p-type doping process and preliminary materials characterization to understand the relationship between substrate quality, epitaxial layer quality, and device performance. Future directions for GaN device development enabled by the availability of bulk substrates will also be discussed, including implications for lateral devices, novel lateral device designs, and fundamental materials work based on the lessons learned from SiC.

High-Gain InAs Planar Avalanche Photodiodes

We report the fabrication of InAs planar avalanche photodiodes (APDs) using Be ion implantation. The planar APDs have a low background doping of 2 × 10 14 cm -3 and large depletion widths approaching 8 μm. The thick depletion width enabled a gain of 330 to be achieved at -26 V at 200 K without inducing a significant tunneling current. No edge breakdown was observed within the APDs. The surface leakage current was found to be low with a gain normalized dark current density of 400 μAcm -2 at -20 V at 200 K

Growth of High Crystalline Quality HVPE-GaN Crystals with Controlled Electrical Properties

Thick free-standing hydride vapor phase epitaxy (HVPE) GaN wafers were grown with close to perfect crystalline quality and with more than two orders of magnitude reduced free carrier concentration relative to ammonothermal GaN without resorting to deep level compensation. These new homoepitaxially grown crystals exceed the quality of any commercially available GaN substrates. High crystalline quality is confirmed by XRD rocking curve measurements having full width at half-maximum of only 16 arc s. Detailed Raman scattering spectroscopy and imaging show that the wafers are biaxially stress-free and have a uniform and low background doping. The stress-free, flat nature of these substrates is essential for high-yield device fabrication. High-resolution photoluminescence studies in combination with SIMS analysis identify Si and O as residual shallow donors with concentration levels orders of magnitude lower than those present in ammonothermal GaN substrates.

Improved GaN films with low background doping and low deep trap density grown by hydride vapor phase epitaxy

AbstractElectrical properties and deep electron and hole traps spectra are compared for undoped n‐GaN films grown by hydride vapor phase epitaxy (HVPE) on sapphire substrates at 850 °C (Group 1) and 950 °C (Group 2). Group 1 samples have very low residual donor concentration ((2‐5)×1014 cm‐3), very low density of electron and hole traps, low leakage current of Schottky diodes. Group 2 samples are not very different from the usual thick HVPE samples in terms of predominant electron and hole traps and MCL spectra. But the concentration of both electron and hole traps is quite high and could contribute to rather high reverse leakage current, low photocurrent and pronounced tunneling. (© 2015 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Gate-induced transition between metal-type and thermally activated transport in self-catalyzed MBE-grown InAs nanowires

Electronic transport properties of InAs nanowires are studied systematically. The nanowires are grown by molecular beam epitaxy on a SiOx-covered GaAs wafer, without using foreign catalyst particles. Room-temperature measurements revealed relatively high resistivity and low carrier concentration values, which correlate with the low background doping obtained by our growth method. Transport parameters, such as resistivity, mobility, and carrier concentration, show a relatively large spread that is attributed to variations in surface conditions. For some nanowires the conductivity has a metal-type dependence on temperature, i.e. decreasing with decreasing temperature, while other nanowires show the opposite temperature behavior, i.e. temperature-activated characteristics. An applied gate voltage in a field-effect transistor configuration can switch between the two types of behavior. The effect is explained by the presence of barriers formed by potential fluctuations.

High-Gain InAs Avalanche Photodiodes

We report two InAs avalanche photodiode structures with very low background doping in the depletion region. Uniform electric fields and thick depletion regions have been achieved. Excess noise measurements are consistent with k~0 and gain as high as 70 at room temperature is observed. The measured gain-bandwidth product is >; 300 GHz. All measurements are consistent with Monte Carlo simulations.

Chloride Based CVD of 3C-SiC on (0001) α-SiC Substrates

A chloride-based chemical-vapor-deposition (CVD) process has been successfully used to grow very high quality 3C-SiC epitaxial layers on on-axis α-SiC substrates. An accurate process parameters study was performed testing the effect of temperature, in situ surface preparation, precursor ratios, nitrogen addition, and substrate polytype and polarity. The 3C layers deposited showed to be largely single-domain material of very high purity and of excellent electrical characteristics. A growth rate of up to 10 µm/h and a low background doping enable deposition of epitaxial layers suitable for MOSFET devices.

Epitaxial Growth and Defect Control of SiC for High-Voltage Power Devices

Recent progress in fast epitaxial growth and defect control of silicon carbide (SiC) toward development of high-voltage power devices is reviewed. In chemical vapor deposition of 4H-SiC on off-axis (0001), a high growth rate of 85 µm/h and a low background doping of 1×1013 cm−3 are achieved. Conversion of basal-plane dislocations to threading edge dislocations and generation of stacking faults during epitaxial growth are discussed. Deep levels in as-grown n-type and p-type 4H-SiC epitaxial layers have been investigated. A lifetime-killing defect, Z1/2 center, can be almost eliminated by thermal oxidation, which leads to significant increase in carrier lifetimes. The obtained carrier lifetimes are long enough to fabricate 10 kV-class bipolar devices. Control of carrier lifetimes by low-energy electron irradiation is demonstrated.

Chloride-Based CVD at High Growth Rates on 3” Vicinal Off-Angles SiC Wafers

Chloride-based growth on on-axis SiC substrates has been studied at higher temperature than typical CVD conditions. The use of chlorinated precursors allows to grow homo-polytypic layers and to achieve high growth rates for thick layers deposition. In this study a vertical reactor with the gas flow inlet at the bottom has been used to grow layers up to 1.5 mm thick. Thanks to the addition of hydrogen chloride (HCl) to the standard precursors mixture, growth rates up to 300 μm/h have been achieved at a process temperature lower than 1900 °C. Very pure layers, micropipe free, and with a low background doping have been grown on 4H and 6H-SiC carbon and silicon-face, respectively, on-axis 3” diameter substrates. The results obtained indicates that this process has the potential to become a novel bulk growth technique at lower temperature than usual, which could give several advantages.

Photocurrent analysis of a fast Ge p-i-n detector on Si

Germanium vertical p-i-n photodetectors grown on silicon with molecular beam epitaxy are investigated. The photocurrent of a high speed detector structure is analyzed at infrared wavelengths of around 1.3μm. The dark current and photocurrent were measured for reverse and forward biased detectors. It is clearly shown that the photocurrent is proportional to the width of the depletion layer. This means that the fast carriers from the depletion layer generate mainly the photocurrent and by this the high speed operation of the germanium detector is explained. Nearly abrupt junctions and low background doping allow zero bias operation of these detectors.

Dilute nitride GaInNAs and GaInNAsSb solar cells by molecular beam epitaxy

Dilute nitride films with a roughly 1 eV band gap can be lattice-matched to gallium arsenide and germanium, and therefore could become a critical component in next-generation multijunction solar cells. To date most dilute nitride solar cells have been plagued with poor efficiency, due in large part to short diffusion lengths. This study focuses on two techniques aimed at improving the quality of dilute nitride films grown by molecular beam epitaxy: the utilization of biased deflection plates installed in front of the nitrogen plasma source, and the introduction of antimony during growth. Results from GaInNAs cells grown with and without deflection plates, and GaInNAsSb solar cells are reported. The use of biased deflection plates during GaInNAs growth improved every aspect of solar cell performance. For the GaInNAs devices grown with deflection plates, the dark current density, open-circuit voltage, and fill factor were the best of the devices studied. The GaInNAsSb cells had the highest quantum efficiency, almost 80% at maximum, mainly due to low background doping densities providing these devices with wide depletion widths. The GaInNAsSb materials also had quite narrow band gaps of 0.92 eV. Because of the high collection efficiency coupled with the narrow band gap, the sub-GaAs short-circuit current density produced by the GaInNAsSb cells is 14.8 mA∕cm2, which was the highest of the devices studied. This current is nearly 50% greater than the best dilute nitride solar cells in the literature, and is the first dilute nitride cell to produce enough current to current match the upper two subcells in a triple-junction device, composed of GaInP/InGaAs/GaInNAsSb.