Structural Modulation of GaN Nanowires Grown in High-Density Plasma Environment

Abstract

We demonstrate a structural modulation method of GaN nanowires (NWs) by microwave plasma chemical vapor deposition. This method is based on the self-assembled growth mode without a harmful gas source and could easily achieve structures with a remarkable range of geometries and sizes by regulating the plasma-phase conditions. The results show that we are able to modulate GaN NWs with a large scale of sizes of lengths from ∼2.2 to 52.4 μm and diameters from ∼22 to 1000 nm. Due to introduce the high-density plasma phase, we propose a new growth and modulation model of GaN NWs via combining the competition and equilibrium of the interface effect, the diffusion effect, and the surface effect. We found that the critical diameter defined by the surface energy has a noteworthy correlation with the growth of NWs due to the significant effect of nitrogen plasma on the surface of NWs. In addition, the photoluminescence performance including the emission peak position, intensity, and full width at half-maximum can be well regulated by the structural effects of GaN NWs. This modulation provides an economical, flexible, and environmentally friendly route to single-crystalline GaN NWs and their devices. Furthermore, the combined growth effect model could provide new physical and chemical insight into the growth mechanism of GaN NWs controlled by high-density plasma.

Photoluminescence Properties of GaN Nanowires Grown in a Gradient-Plasma Environment

“…According to the VLS mechanism, the growth rate is given by the Givargizov–Chernov (GC) model neglecting the diffusion effects: − where b is the kinetic coefficient of crystallization independent of supersaturation, k is Boltzmann’s constant, T is the growth temperature, Δμ represents supersaturation of nanoscale GaN, Δ μ 0 is supersaturation of bulk GaN, α is the specific free energy of the NW surface, and Ω is the molecular volume of GaN NW. By analyzing the relationship between ν 1/2 and 1/ d as shown in Figure j, the growth state of NWs in RG-2 and 3 is affected by the high-density plasma environment consistent with our previous study . The plasma content thus has a significant effect on NW growth and the Ga-rich environment is more conducive to the growth of high-quality GaN NWs.…”

“…By analyzing the relationship between ν 1/2 and 1/d as shown in Figure 2j, the growth state of NWs in RG-2 and 3 is affected by the high-density plasma environment consistent with our previous study. 21 The plasma content thus has a significant effect on NW growth and the Ga-rich environment is more conducive to the growth of high-quality GaN NWs.…”

“…The GaN NWs were fabricated by MPCVD in a gradient nitrogen plasma environment with an improved homemade quartz crucible and quartz cover. Compared to the original one, the improved homemade quartz crucible and quartz cover were more conductive to place a vertical substrate . The mixed powder of Ga 2 O 3 (99.999% pure) and carbon (99.99% pure) powders with a Ga 2 O 3 : C mass ratio of 1:6 was placed in the quartz crucible.…”

“…Compared to the original one, the improved homemade quartz crucible and quartz cover were more conductive to place a vertical substrate. 21 The mixed powder of Ga 2 O 3 (99.999% pure) and carbon (99.99% pure) powders with a Ga 2 O 3 : C mass ratio of 1:6 was placed in the quartz crucible. A 10 mm × 20 mm silicon (100) substrate with a 15 nm thick Au film was positioned vertically in the center of the quartz crucible.…”

Wrinkled‐Surface‐Induced Memristive Behavior of MoS2 Wrapped GaN Nanowires

“…Figure a illustrates the preparation process diagram of the MoS 2 ‐GaN NWs memristor. The memristive layer in this two‐terminal device is fabricated on the silicon (Si) substrate by plasma enhanced chemical vapor deposition (PECVD) [ 21–23 ] and magnetron sputtering and to obtain a stable top electrode structure, spray coating is performed with the Ag NWs solution. The side‐ and top‐view SEM images of the MoS 2 ‐GaN NWs and pure GaN NWs are depicted in Figure 1b–e showing that MoS 2 is coated around the NWs.…”