Muhammad Ali Johar

Facile growth of density- and diameter-controlled GaN nanobridges and their photodetector application

The growth of arrayed GaN nanobridges (NBs) and their application in a photodetector (PD) were studied. First, GaN nanowires (NWs) were selectively grown on the sidewalls of a GaN mesa using an Au catalyst-assisted vapor–liquid–solid (VLS) method, while their density was conveniently controlled by varying the dilution of the Au nanoparticle colloidal solution. It was revealed that an m-axis NW was preferentially fabricated on both the m-plane and a-plane sidewalls. A two-step VLS–VS growth technique was utilized for the radial core–shell structure composed of GaN, InGaN and InGaN/GaN multi-quantum wells (MQWs) that allowed independent control of the NW diameter. Finally, core–shell NBs were fabricated across a trench formed between two GaN mesas to be used as a light absorbing medium in a photoconductor. Their optical response was measured at various wavelengths and InGaN/GaN MQWs embedded in the core–shell structure exhibited an enhanced photoresponse to visible light.

Stable and High Piezoelectric Output of GaN Nanowire-Based Lead-Free Piezoelectric Nanogenerator by Suppression of Internal Screening

A piezoelectric nanogenerator (PNG) that is based on c-axis GaN nanowires is fabricated on flexible substrate. In this regard, c-axis GaN nanowires were grown on GaN substrate using the vapor-liquid-solid (VLS) technique by metal organic chemical vapor deposition. Further, Polydimethylsiloxane (PDMS) was coated on nanowire-arrays then PDMS matrix embedded with GaN nanowire-arrays was transferred on Si-rubber substrate. The piezoelectric performance of nanowire-based flexible PNG was measured, while the device was actuated using a cyclic stretching-releasing agitation mechanism that was driven by a linear motor. The piezoelectric output was measured as a function of actuation frequency ranging from 1 Hz to 10 Hz and a linear tendency was observed for piezoelectric output current, while the output voltages remained constant. A maximum of piezoelectric open circuit voltages and short circuit current were measured 15.4 V and 85.6 nA, respectively. In order to evaluate the feasibility of our flexible PNG for real application, a long term stability test was performed for 20,000 cycles and the device performance was degraded by less than 18%. The underlying reason for the high piezoelectric output was attributed to the reduced free carriers inside nanowires due to surface Fermi-level pinning and insulating metal-dielectric-semiconductor interface, respectively; the former reduced the free carrier screening radially while latter reduced longitudinally. The flexibility and the high aspect ratio of GaN nanowire were the responsible factors for higher stability. Such higher piezoelectric output and the novel design make our device more promising for the diverse range of real applications.

Correction to: Facile morphology control of high aspect ratio patterned Si nanowires by metal-assisted chemical etching

The original version of this article unfortunately contained an error in one of the co-author’s name. Part of family name was erroneously tagged as given name. The correct name should be “Mostafa Afifi Hassan”.

Facile morphology control of high aspect ratio patterned Si nanowires by metal-assisted chemical etching

Facile and effective method to fabricate highly ordered silicon nanowires (SiNWs) using metal-assisted chemical etching (MACE) was demonstrated. MACE solutions with various concentrations were studied to understand the etching mechanism for patterned Si substrates with different doping concentrations. MACE rate of Si (100) at different time periods was studied with different doping concentrations (p, p+, n, and n+) at a MACE solution concentration of 5:1:1 for an accurate morphology control and reproducibility of the SiNWs. Based on a four-step model, the SiNW formation mechanism was proposed involving anisotropic etching of SiNWs based on hole transfer between Au/Si interfaces exposed when subjected to MACE solution. Time dependent variation in etch rate of Si to fabricate SiNWs was observed with different doping concentration. The effect of the doping concentration on the etching was revealed based on band diagrams. However, agglomeration of p+-SiNWs was observed, which was attributed to their doping and ability to act against various forces like surface tension during drying. Different aspect ratios of SiNWs were observed for different time periods; n+-SiNWs exhibited the maximum aspect ratio of approximately 81. A visible-light absorbance analysis revealed the potential of the synthesized SiNWs can be good base and host materials for various light harvesting and energy storage devices.