Growth and characterization of tree-like crystalline structures during electrochemical formation of porous GaN

Electrochemical etching of crystalline n-GaN in H2SO4:H2O2 results in the formation of porous GaN. Scanning electron microscopy images revealed the presence of branches on the surface of porous GaN and showed the varying stages with etching time. The branches on the surface of the porous GaN that have been associated with Ga2O3 have a significant enhancing effect on the photoluminescence intensity. Raman spectra of both as-grown and porous GaN exhibit phonon mode E2 (high), A1 (LO), A1 (TO) and E2 (low). There is a red shift in E2 (high), indicating a relaxation of compressive stress in the porous GaN surface with respect to the underlying single-crystalline epitaxial GaN

Effect of different electrolytes on porous GaN using photo-electrochemical etching

This article reports the properties and the behavior of GaN during the photoelectrochemical etching process using four different electrolytes. The measurements show that the porosity strongly depends on the electrolyte and highly affects the surface morphology of etched samples, which has been revealed by scanning electron microscopy (SEM) images. Peak intensity of the photoluminescence (PL) spectra of the porous GaN samples was observed to be enhanced and strongly depend on the electrolytes. Among the samples, there is a little difference in the peak position indicating that the change of porosity has little influence on the PL peak shift, while it highly affecting the peak intensity. Raman spectra of porous GaN under four different solution exhibit phonon mode E2 (high), A1 (LO), A1 (TO) and E2 (low). There was a red shift in E2 (high) in all samples, indicating a relaxation of stress in the porous GaN surface with respect to the underlying single crystalline epitaxial GaN. Raman and PL intensities were high for samples etched in H2SO4:H2O2 and KOH followed by the samples etched in HF:HNO3 and in HF:C2H5OH

Synthesis, structural, and optical properties of electrochemically deposited GeO2 on porous silicon

We present a method to synthesize submicrometer germanium dioxide (GeO2) on porous silicon (PS) by electrochemical deposition. The PS was electrochemically prepared in HF based electrolyte. GeCl4 was directly hydrolyzed by hydrogen peroxide to produce pure GeO2 and then electrochemically deposited on PS. The scanning electron microscopy results showed that the GeO2 structures are uniform in shape with diameter ∼500 nm. The photoluminescence spectrum showed a prominent peak related to GeO2 at about 400 nm. The results indicated potential applications of GeO2 on the silicon based substrate for future optoelectronic nanodevices in the visible region using a simple fabrication method

Characterization of Ge nanostructures embedded inside porous silicon for photonics application

In this work we prepared germanium nanostructures by means of filling the material inside porous silicon (PS) using conventional and cost effective technique, thermal evaporator. The PS acts as patterned substrate. It was prepared by anodization of silicon wafer in ethanoic hydrofluoric acid (HF). A Ge layer was then deposited onto the PS by thermal evaporation. This was followed by deposition of Si layer by thermal evaporation and anneal at 650°C for 30 min. The process was completed by Ni metal deposition using thermal evaporator followed by metal annealing of 400°C for 10 min to form metal semiconductor metal (MSM) photodetector. Structural analysis of the samples was performed using energy dispersive x-ray analysis (EDX), scanning electron microscope (SEM), X-ray diffraction (XRD) and Raman spectroscopy (RS). EDX spectrum suggests the presence of Ge inside the pores structure. Raman spectrum showed that good crystalline structure of Ge can be produced inside silicon pores with a phase with the diamond structure by (111), (220) and (400) reflections. Finally current-voltage (I- V) measurement of the MSM photodetector was carried out and showed lower dark currents compared to that of Si control device. Interestingly the device showed enhanced current gain compared to Si device which can be associated with the presence of Ge nanostructures in the porous silicon

High sensitivity of palladium on porous silicon MSM photodetector

In this work, the nanocrystalline porous silicon (PS) is prepared through the simple electrochemical etching of n-type Si (1 0 0) under the illumination of a 100 W incandescent white light. SEM, AFM, Raman and PL have been used to characterize the morphological and optical properties of the PS. SEM shows uniformed circular pores with estimated sizes, which range between 100 and 500 nm. AFM shows an increase in its surface roughness (about 6 times compared to c-Si). Raman spectra of the PS show a stronger peak with FWHM=4.3 cm -1 and slight blueshift of 0.5 cm -1 compared to Si. The room temperature photoluminescence (PL) peak corresponding to red emission is observed at 639.5 nm, which is due to the nano-scaled size of silicon through the quantum confinement effect. The size of the Si nanostructures is estimated to be around 7.8 nm from a quantized state effective mass theory. Thermally untreated palladium (Pd) finger contact was deposited on the PS to form MSM photodetector. Pd/PS MSM photodetector shows lower dark (two orders of magnitude) and higher photocurrent compared to a conventional Si device. Interestingly, Pd/PS MSM photodetector exhibits 158 times higher gain compared to the conventional Si device at 2.5 V