The Effect of Etching Time On Structural Properties of Porous Quaternary AlInGaN Thin Films

Using photo electrochemical etching technique (PEC), porous silicon (PS) layers were produced on n-type silicon (Si) wafers to generate porous silicon for n-type with an orientation of (111) The results of etching time were investigated at: (5,10,15 min). X-ray diffraction experiments revealed differences between the surface of the sample sheet and the synthesized porous silicon. The largest crystal size is (30 nm) and the lowest crystal size is (28.6 nm) The analysis of Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscope (FESEM) were used to research the morphology of porous silicon layer. As etching time increased, AFM findings showed that root mean square (RMS) of roughness and porous silicon grain size decreased and FESEM showed a homogeneous pattern and verified the formation of uniform porous silicon.


Introduction
Porous silicon was discovered in 1956 by Ulhir [1] when performing electropolishing silicon wafer experiments using an electrolyte-containing hydrofluoric acid [2]. Porous Silicon (PS) is a silicon-based nanostructured material formed by electrical processing. Silicon remains uniformly undissolved but it creates very fine holes. Electrochemical dissolution of silicon wafers in aqueous or ethanoic solutions has resulted in PS formation. Interest in PS grew in the 1970s and 1980s because its high surface area was found to be useful in spectroscopic studies as a model of the crystalline silicon surface [3]. Leigh Canham reported his findings on red luminescence in the 1990s [4] showing that certain PS materials can have high PL efficiencies at rooms temperatures in the visible. A shocking finding because PL efficiencies of bulk silicon is very low due to its indirect energy bandgap and limited non-radiative lifespan. The reasons for the partial breakdown of silicon which induces the formation of silicon. Phenomena in quantum confinement result in new effects such as photoluminescence or electroluminescence [ 5 ] . PS categories to the diameter of the pore which can be ranged from a few nanometers to a few macrons that depending on the formation parameters [6].
Due to its specific electrical chemical and mechanical features, PS has been shown to achieve effective visible light emissions at room temperature. Different conclusions however are stated on PL from the surface of PS [7,8]. The first concerns the effect of quantum containment due to the charge carriers in the thin crystalline silicon wall that separates the pore walls. Lately several other alternative models were proposed based on hydrogenated amorphous silicon surface hydrides holes' siloxane and surface states [9,10]. Many of the PS layer's properties depends on the etched parameters including HF concentration current density temperature and form and resistivity of the Si wafer [11]. Nitride material system has several important properties 78 that make it ideal for near IR to deep UV optoelectronic devices. These properties also allow AlInGaN material to endure challenging applications that involve harsh operating conditions. An III-nitride semiconductor has a wide direct band gap which can be tuned from 0.7 eV for InN, to 3.5 eV for GaN and to 6.23 eV for AlN. Due to its amazing properties III-nitride groups have gained many great attention in the last few years but the methods to prepare high-quality layer without defects and crystal impurities are only at the beginning and need to be more researched and investigated. One of these methods is: Molecular beam epitaxy (MBE) which was used in this analysis to enable the researchers to improve their commitment to find out new methods in terms of preparation [12]. In this work we Study the structural properties of quaternary AlInGaN thin films.

Experimental work
Quaternary AlInGaN films were deposited on silicon substrate by molecular beam epitaxy the preparation of the n-PS layer is shown in Fig.1 HF main electrolyte acid. And in a horizontal configuration the appliance is built also on n-Si <111> substrates in an electrolyte an HF mixture (40%) is produced from porous silicon generated with a standard technique the all processing during PS formations can be expresses: Anodization is used in the (current-controlled) galvanostatic mode. It is generally favored since irrespective of any evolution during cell electrical impedance anodization it provides the necessary charge for the reaction at a constant pace eventually contributing to homogeneous and reproducible content. It can be modulated by anodization. The modulation is done more effectively by adjusting The PS samples were synthesized by anodic etching using a traditional single-tank electrolyzation cell on n-type Si wafers. Along the (111) crystal plane path, the wafers were polished. The electrolytes were prepared by combining varying volumetric ratios of HF solution and absolute methanol (CH3OH).

Figure 1: The schematic diagram of experimental step for preparing n-PS layer vertical arrangement.
The cell that can be used for silicon anodizing is very simple. The anode is silicon wafer. While the cathode is made of platinum or other substance that is HF resistant and conducting. The distance from the center to the platinum Si is round 2 cm. The silicon wafers used were n-type, <111> double polished with a resistance of 25.cm A selfmade Teflon cell was used to etch a circular area of 1.5 cm 2 on the wafer. By the scribe and cut process the wafers were cut into pieces sufficient to contain this area. Until drying the Si wafer had to be diced first 1.5 to 1.5 cm 2 samples. To extract particulate matter as well organic metallic and ionic contaminants from specimens cleaning is necessary. Aluminum foil is coated with the whole rear half of the aluminum foil as the backside. They jointly sandwiched the sample and aluminum foil into the cell. The wafers were used as usual little was done either on the front side or on the back side. Then the wafer controllable parameters wafer becomes HF concentration time of anodization and illumination. Thus the concentration of HF and the duration of anodization differ. N-type silicon wafers in the experiments. Methanol is used in samples and alcohol is commonly used to disinfect the wafers by immersing it in these chemicals for a few minutes in the ultrasonic baths. Finally, they were rinsed in ultrasonically filtered purified water accompanied by drying in a stream of hot air. Porous silicon (PS) samples were prepared by anodization at a constant time of 5 min, 10 min and 15 min at a current density (50) mA/cm 2 . A photon source, such as halogen lamb, is needed to obtain the nano crystalline porous Si on n-type silicon. An illumination system where the halogen lamb power is 100 watts and the distance between the lamb and Si and intensive light is used to supply the necessary holes. The most effective method of creating holes in the process of electrochemical etching is shown in Fig.2.

Results and discussions
The X-ray diffraction spectra of porous on the n-Si substrate at different etching times are shown in Fig.3. These revealed a separate distinction samples at different anodization between the times based on the phases of the sample the X-ray radiation diffracts at various angular angles with respect to the incident beam. An expansion of diffraction peaks was found as the crystal size was decreased to the nanometer scale and the diameter of the peak closely associated with the size of the peak. Fig.3 also shows the X ray diffraction pattern of AlInGaN after etching time of 5, 10 and 15 min, which revealed that at all cases the diffraction peaks were at 2θ, equal to 34.46, 34.45 and 34.44 corresponding to Si (111), quaternary AlInGaN (0002), buffer layer AlN (002) and AlInGaN (004) respectively. In addition, the intensity of preferred orientation AlInGaN (002) became lower with increasing the etching time while at orientation are reverse which attributed to less the preferring of orientation (002) and formed Nano particles depending of the pores sites added and sequent the quantum confinement effect become very clear.

Conclusions
Quaternary AlInGaN thin films were deposited on silicon substrate by molecular beam epitaxy using N-type porous silicon synthesized by electrochemical etching at different etching times (5, 10 and 15) min. X-ray diffraction patterns showed the formation of porous silicon and that the structure thin film size increase of the Si nanosized of the Si peaks the particle size of the porous layers is nanostructured were decrease. The investigation of atomic force microscopy has demonstrated an improvement in surface roughness with the increase of etching time. Field Emission scanning electron microscope (FESEM) of PS at various etching periods revealed, a homogeneous pattern and confirmed the development of uniform porous structures on the silicon wafers.