title: Controlled vapor phase growth of single crystalline, two-dimensional GaSe crystals with high photoresponse.
abstract: Compared with their bulk counterparts, atomically thin two-dimensional (2D) crystals exhibit new physical properties, and have the potential to enable next-generation electronic and optoelectronic devices. However, controlled synthesis of large uniform monolayer and multi-layer 2D crystals is still challenging. Here, we report the controlled synthesis of 2D GaSe crystals on SiO2/Si substrates using a vapor phase deposition method. For the first time, uniform, large (up to ~60 μm in lateral size), single-crystalline, triangular monolayer GaSe crystals were obtained and their structure and orientation were characterized from atomic scale to micrometer scale. The size, density, shape, thickness, and uniformity of the 2D GaSe crystals were shown to be controllable by growth duration, growth region, growth temperature, and argon carrier gas flow rate. The theoretical modeling of the electronic structure and Raman spectroscopy demonstrate a direct-to-indirect bandgap transition and progressive confinement-induced bandgap shifts for 2D GaSe crystals. The 2D GaSe crystals show p-type semiconductor characteristics and high photoresponsivity (~1.7 A/W under white light illumination) comparable to exfoliated GaSe nanosheets. These 2D GaSe crystals are potentially useful for next-generation electronic and optoelectronic devices such as photodetectors and field-effect transistors.
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN, 37831, USA.
authors: Xufan
authors: X
authors: Li
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN, 37831, USA.
authors: Ming-Wei
authors: MW
authors: Lin
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN, 37831, USA.
authors: Alexander A
authors: AA
authors: Puretzky
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN, 37831, USA.
authors: Juan C
authors: JC
authors: Idrobo
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN, 37831, USA.
authors: Cheng
authors: C
authors: Ma
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN, 37831, USA.
authors: Miaofang
authors: M
authors: Chi
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN, 37831, USA.
authors: Mina
authors: M
authors: Yoon
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN, 37831, USA.
authors: Christopher M
authors: CM
authors: Rouleau
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN, 37831, USA.
authors: Ivan I
authors: II
authors: Kravchenko
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN, 37831, USA.
authors: David B
authors: DB
authors: Geohegan
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN, 37831, USA.
authors: Kai
authors: K
authors: Xiao