A two-colour heterojunction unipolar nanowire light-emitting diode by tunnel injection

Abstract

We present a systematic study of the current-voltage characteristics and electroluminescence of gallium nitride (GaN) nanowire on silicon (Si) substrate heterostructures where both semiconductors are n-type. A novel feature of this device is that by reversing the polarity of the applied voltage the luminescence can be selectively obtained from either the nanowire or the substrate. For one polarity of the applied voltage, ultraviolet (and visible) light is generated in the GaN nanowire, while for the opposite polarity infrared light is emitted from the Si substrate. We propose a model, which explains the key features of the data, based on electron tunnelling from the valence band of one semiconductor into the conduction band of the other semiconductor. For example, for one polarity of the applied voltage, given a sufficient potential energy difference between the two semiconductors, electrons can tunnel from the valence band of GaN into the Si conduction band. This process results in the creation of holes in GaN, which can recombine with conduction band electrons generating GaN band-to-band luminescence. A similar process applies under the opposite polarity for Si light emission. This device structure affords an additional experimental handle to the study of electroluminescence in single nanowires and, furthermore, could be used as a novel approach to two-colour light-emitting devices.

ZnO nanorod/GaN light-emitting diodes: The origin of yellow and violet emission bands under reverse and forward bias

“…Tunneling phenomena in III-nitride heterojunctions have been previously observed for different material combinations. [48][49][50][51] Furthermore, since the lattice mismatch between GaN and ZnO is higher than 1%, interface states are expected to significantly affect the current flow across the junction and severely limit the injection of the minority carriers. 52 Thus, significant current transport mechanisms in these devices are expected to involve tunneling and recombination at the interface, 52 and the tunneling likely involves the defect states at the interface, as illustrated in Fig.…”

Exciton-related electroluminescence from ZnO nanowire light-emitting diodes

“…8 An even more intriguing prospect is that of combining widely different semiconductor materials, such as direct band-gap materials and silicon, without the need for wafer bonding technology. [10][11][12] In particular, we have recently demonstrated the fabrication of nanowire light-emitting diodes ͑LEDs͒ on a heavily-doped p-type silicon ͑p-Si͒ substrate, using nanowires of the wide-band-gap semiconductor zinc oxide ͑ZnO͒. ZnO is a material well suited for the development of ultraviolet ͑UV͒ optoelectronic devices 13 due to its large exciton binding energy.…”

“…12 If the p-Si native oxide is not removed before the fabrication of the nanowire devices, it acts as a tunnel barrier between the two semiconductors. 10,11 With an applied external bias, holes can tunnel from the valence band of the p-Si into the valence band of the ZnO nanowire. For such devices, UV electroluminescence ͑EL͒ has been observed at room temperature with the output intensity showing an almost linear dependence on the current flowing through the nanowire LED.…”

Polarity-controlled visible/infrared electroluminescence in Si-nanocrystal/Si light-emitting devices

“…3,4 Here, we report the demonstration of color-switchable Si-nc LEDs that take advantage of visible emission from silicon nanocrystals and infrared from the Si substrate. 5,6 We show that the emission bands of devices can be controlled by the polarity of applied bias voltage: infrared under forward bias, and visible under reverse bias.…”

“…Si band-edge infrared emission and visible EL have been observed in different MIS structures [3][4][5][6][7][8][9] and Si-nanocrystal LEDs. [10][11][12] In general, emission spectra and the associated microscopic origins strongly depend on the material, device configuration, and operating condition.…”