III–N–V semiconductors are promising materials for use in next-generation multijunction solar cells because these materials can be lattice matched to substrates such as GaAs, Ge and Si, with a range of bandgaps that are complementary to those of other III–V semiconductors. Several potentially high-efficiency multijunction photovoltaic device designs using III–N–V materials are discussed. The main roadblock to the development of these solar cell devices is poor minority-carrier transport in the III–N–V materials. The present understanding of the material properties of GaInNAs lattice matched to GaAs and GaNPAs lattice matched to Si is reviewed.

https://iopscience.iop.org/article/10.1088/0268-1242/17/8/305/pdf

III-N-V semiconductors for solar photovoltaic applications

A comparison of MBE- and MOCVD-grown GaInNAs

The effects of H on the interaction between Ga vacancies ${V}_{\mathrm{Ga}}$ and N in ${\mathrm{GaAs}}_{1\ensuremath{-}x}{\mathrm{N}}_{x}$ dilute alloys are studied through first-principles total-energy calculations. We find that N binds to Ga vacancies and that in the presence of H this binding is enhanced. The formation energy of ${V}_{\mathrm{Ga}}$ bonded to N and H (resulting in a $\mathrm{N}\ensuremath{-}\mathrm{H}\ensuremath{-}{V}_{\mathrm{Ga}}$ complex) can be more than 2 eV lower than that of the isolated Ga vacancy ${V}_{\mathrm{Ga}}$ in GaAs. Our finding that the concentration of ${V}_{\mathrm{Ga}}$ increases with N and even more in the presence of H allows us to interpret several recent experiments.

Interactions between nitrogen, hydrogen, and gallium vacancies in GaAs 1-x N x alloys

Using solid-source molecular-beam epitaxy with a rf-plasma source, we have grown GaInNAs/GaAs single-quantum-well lasers operating at 1.32 μm. For a broad-area oxide stripe, uncoated Fabry–Perot laser with a cavity length of 1600 μm, the threshold current density is 546 A/cm2 at room temperature. The internal quantum efficiency for these lasers is 80%, while the materials losses are 7.0 cm−1. A characteristic temperature of 104 K was measured in the temperature range from 20 to 80 °C. Optical output up to 40 mW per facet under continuous-wave operation was achieved for these uncoated lasers at room temperature.

Low-threshold-current 1.32-μm GaInNAs/GaAs single-quantum-well lasers grown by molecular-beam epitaxy

We have investigated by photoluminescence spectroscopy and x-ray diffraction the influence of ex situ postgrowth annealing on the properties of a series of dedicated Ga(In)(N)As ternary and quaternary quantum wells (QWs) confined by various barrier layers. We show that the low growth temperature and not N per se, is largely responsible for the low radiative efficiency of Ga(In)NAs QWs. Furthermore, postgrowth annealing induces a blueshift of the photoluminescence line in the case of quaternary GaInNAs QWs only, while x-ray diffraction reveals the absence of compositional change. We conclude with the occurrence of a local reorganization of the N-bonding configuration within the GaInNAs quaternary material during annealing.

Mechanisms affecting the photoluminescence spectra of GaInNAs after post-growth annealing

Positron-annihilation measurements and nuclear reaction analysis [utilizing the 14N(d,p)15N and 14N(d,He)12C reactions] in conjunction with Rutherford backscattering spectrometry in the channeling geometry were used to study the defects in as-grown Ga(In)NAs materials grown by molecular beam epitaxy using a radio-frequency plasma nitrogen source. Our data unambiguously show the existence of vacancy-type defects, which we attribute to Ga vacancies, and nitrogen interstitials in the as-grown nitride–arsenide epilayers. These point defects, we believe, are responsible for the low luminescence efficiency of as-grown Ga(In)NAs materials and the enhanced diffusion process during annealing.

James Decker

Papers

Origin of improved luminescence efficiency after annealing of Ga(In)NAs materials grown by molecular-beam epitaxy