Nanosails Showcasing Zn₃As₂ as an Optoelectronic‐Grade Earth Abundant Semiconductor

Abstract

Zn 3 As 2 is a promising earth-abundant semiconductor material. Its bandgap, around 1 eV, can be tuned across the infrared by alloying and makes this material suited for applications in optoelectronics. Here, we report the crystalline structure and electrical properties of strain-free Zn 3 As 2 nanosails, grown by metal-organic vapor phase epitaxy. We demonstrate that the crystalline structure is consistent with the P4 2 /nmc (D 15 4h ) α"-Zn 3 As 2 metastable phase. Temperature-dependent Hall effect measurements indicate that the material is degenerately p-doped with a hole mobility close to 10 3 cm 2 V À1 s À1 . Our results display the potential of Zn 3 As 2 nanostructures for next generation energy harvesting and optoelectronic devices.The increasing production of high-performance electronic devices and the push towards generating energy in a sustainable manner leads to sustainability challenges for optoelectronic and photovoltaic (PV) technologies. Particularly affected are devices using atomic elements of scarce abundance in the earth's crust, which prevents their widespread deployment. In this context, highly functional materials made of earth-abundant elements are being sought for both PV and optoelectronic applications. The second most abundant element in the earth's crust, silicon, is a semiconductor very successfully deployed in the PV market. It suffers nonetheless from its indirect bandgap and the consequently high purity required for the production of efficient solar cells. Both characteristics increase the energy needs for silicon PV device production. The so-called "second generation" solar cells, built with much thinner, direct bandgap active layers, could in principle solve these two issues. Still, these thin film solar cells exhibit either a long energy payback time (amorphous silicon) or they use scarce and expensive elements (ex: copper, indium, gallium, selenium, cadmium, tellurium).Direct bandgap semiconductors employing earth-abundant elements could combine the advantages of all these material families. They would enable efficient light collection in a thin film of easily available materials. Copper zinc tin sulfide (CZTS) and zinc phosphide (Zn 3 P 2 ) have received increasing attention as materials satisfying these criteria for efficient and sustainable light conversion discussed so far. Belonging to the same family, zinc arsenide (Zn 3 As 2 ) is a p-type semiconductor structurally similar to Zn 3 P 2 . It exhibits a band gap around 1.0 eV [1] and potentially high hole mobilities. [2] The stoichiometry of this material can be transformed continuously into Cd 3 As 2 [3] or Zn 3 P 2[4] by appropriate atomic substitutions, shifting its bandgap energy toward 1.5 eV and 0 eV, respectively. (Zn 1Àx Cd x ) 3 As 2 transforms from a semiconductor to a threedimensional Dirac semimetal as x reaches 0.62. [5] The ability to tune its direct bandgap energy makes this material system very attractive for long-wavelength optoelectronics and as a constituent in multi-junction solar cells. M II 3 X V 2 comp...

Showcasing the optical properties of monocrystalline zinc phosphide thin films as an earth-abundant photovoltaic absorber

“…The presence of an impurity band has already been shown to exist in Zn 3 As 2 , a II–V semiconductor structurally and electronically similar to Zn 3 P 2 . 46 The critical defect concentration for the Mott transition in Zn 3 P 2 and Zn 3 As 2 are similar and may be around 2 × 10 16 cm −3 . 47…”

“…by the Royal Society of Chemistry structurally and electronically similar to Zn 3 P 2 . 46 The critical defect concentration for the Mott transition in Zn 3 P 2 and Zn 3 As 2 are similar and may be around 2 Â 10 16 cm À3 . 47 One of the most common defects in zinc phosphide, and most especially in phosphorus-rich crystals, are phosphorus interstitials.…”

Multiple morphologies and functionality of nanowires made from earth-abundant zinc phosphide

“…[16][17][18] These factors mitigate the challenges posed by II 3 V 2 's large lattice parameter and coefficient of thermal expansion, facilitating virtually defect-free epitaxial growth. 19,20 Moreover, vertical nanowire arrays exhibit photonic properties enabling increased light absorption with respect to the equivalent thin film. [21][22][23][24][25][26][27][28][29] This is a consequence of their enhanced absorption cross-section, and modification of light emission directivity.…”

Regaining a Spatial Dimension: Mechanically Transferrable Two-Dimensional InAs Nanofins Grown by Selective Area Epitaxy

“…More recently, trench structures in a SiO x mask have been used to grow long horizontally-oriented InAs, [32][33][34][35][36][37] GaN, 38 GaAs, 24,37,39 and InSb 43 nanowires, along with more exotic materials. 44 These structures remain on their growth substrate for use as photonic structures, 24,[38][39][40][41][42] electronic wires [33][34][35]43 or as templates for further growth, e.g., InAs nanowires atop GaAs nanomembranes. 45 Our focus sits in a currently untapped space between the works described above -we seek the large open areas of the 2D 'sail-like' structures from catalyst-driven VLS growth but with the precise shape control and uniformity available from selective-area epitaxy and the ability to transfer the structures to a separate substrate for device fabrication.…”