Intrinsically p-type cuprous iodide semiconductor for hybrid light-emitting diodes

Abstract

Cuprous halides, characterized by a direct wide band-gap and a good lattice matching with Si, is an intrinsic p-type I-VII compound semiconductor. It shows remarkable optoelectronic properties, including a large exciton binding energy at room temperature and a very small piezoelectric coefficient. The major obstacle to its application is the difficulty in growing a single-crystal epitaxial film of cuprous halides. We first demonstrate the single crystal epitaxy of high quality cuprous iodide (CuI) film grown on Si and sapphire substrates by molecular beam epitaxy. enhanced photoluminescence on the order of magnitude larger than that of GaN and continuous-wave optically pumped lasing were found in MBE grown CuI film. The intrinsic p-type characteristics of CuI were confirmed using an n-AlGaN/p-CuI junction that emits blue light. The discovery will provide an alternative way towards highly efficient optoelectronic devices compatible with both Si and III-nitride technologies. Cuprous halide atoms form a tetrahedrally coordinated isomorphic structure with the diamond-type lattice 1-16. The Cu atoms are located on a face-centered cubic lattice, and the four nearest neighboring sites are occupied by halogen-type atoms, as shown in Fig. 1(a), which forms a zinc blende structure 8,17-26. The zinc blende structure minimizes the piezoelectric effect resulting from polarization because it has four symmetry-equivalent polar axes and each electrical field contribution cancels each other. A semiconductor is polarized if it has a singular polar axis as in the case of the [0001] axis for wurtzite semiconductors, such as gallium nitride (GaN) and zinc oxide (ZnO) 27-35. It is well known that the luminous efficiency of wurtzite structure is significantly affected by the presence of polarization. Large built-in electrostatic fields of the order of MV/cm in the active layer will result in long radiative lifetimes 28-35. Since the piezoelectric effect of cuprous halides is much smaller than that of III-nitrides, we can easily ignore piezoelectric field effects for cuprous halide semiconductors, which is a great advantage for optoelectronic applications 1,23. Moreover, the large lattice mismatch between the nitride semiconductor and the commercially available substrates, typically sapphire or SiC, inevitably generates a high misfit dislocation density in the order of 10 10 cm −2. The performance and reliability of the device would be degraded. Although a lot of epitaxial growth technologies have been developed to minimize misfit dislocation density, it is still suffered from the high density of defects which prevents realization of high performance electronic and optical devices on nitride semiconductor 2,4,16,20. It would be desirable to have a kind of semiconductor with good lattice match to Si for the purpose.

Engineering Copper Iodide (CuI) for Multifunctional p‐Type Transparent Semiconductors and Conductors

“…Bottom images: Reproduced with permission. [ 145 ] Copyright 2020, Nature Publishing Group. Top image: Reproduced with permission.…”

“…Benefiting from the large exciton binding energy of CuI, that is, 58 meV, CuI has recently been employed in highly efficient blue and UV LEDs and is expected to replace commercialized GaN in the future. [ 144 , 145 , 146 ] In 2020, Ahn et al. grew epitaxial p‐CuI as a hole injection layer and reported a hybrid n‐GaN/p‐CuI blue LED.…”

“…grew epitaxial p‐CuI as a hole injection layer and reported a hybrid n‐GaN/p‐CuI blue LED. [ 145 ] The epitaxial CuI showed superior electrical properties as compared to the early developed p‐GaN for commercial LEDs. A stronger photoluminescence peak intensity was also observed in the CuI film.…”

Prediction and realisation of high mobility and degenerate p-type conductivity in CaCuP thin films

“… 19 Thin films of CuI have been trialled successfully as thin film transistors, 22 while single crystals of CuI have recently been grown for the first time, capable of acting as a hybrid blue LED. 23 The facile deposition, wide direct band gap, self-doping mechanism (under I-rich conditions) and absence of secondary phases make CuI a very attractive p-type transparent conducting non-oxide.…”

Predicting Solid State Material Platforms for Quantum Technologies

“…To the best of our knowledge, ZnCd 3 Se 4 has yet to be synthesized, while self-assembled InAs quantum dots are exciting possible materials to use in quantum technology [76]. CuI has recently been synthesized as single-crystal epitaxial films and was shown to exhibit remarkable optoelectronic properties [77]. Interestingly, the material exhibits a large ionic character with more similarities to some of the oxide compounds in the dataset than, e.g., the materials that are more covalent in character like Si, SiC and diamond.…”