Abstract
The PL of porous GaN sample shows higher intensity with smaller FWHM and red-shifting relative to the as-grown sample. The energy gap for porous GaN sample was smaller compare to the as-grown sample. The SEM surface image of UV-assisted electrochemical etching process is shown a shape and size of pore which was formed on the surface of the GaN, therefore the shape of pores formed was in spherical shape. The size of the pores formed has diameter as small as 85 nm. Two PL peaks were observed in the as-grown and porous GaN sample. For the as-grown GaN, the higher peak was observed at “361.946 nm” and the other at “723.739 nm” which is in UV and red luminescence region respectively. The FWHM is “8.198 nm” at “361.946 nm”. For the porous GaN, the higher peak was observed at “364.235 nm” and at “728.039 nm”, so their FWHM are “4.244 nm” and “8.926 nm” respectively. The peaks of porous sample were red-shifted at “2.289 nm and 4.30 nm” respectively compare to the peaks of the as-grown GaN. PL intensity of the porous samples was observed to be increased. Raman peaks representative to the wurtzite GaN crystal, namely E 2 (low) at 142.426 cm -1 , E 2 (high) at 568.771 cm -1 , and A 1 (LO) at 736.769 cm -1 were clearly observed.
Highlights
Porous semiconductors show various important optical features compare to normal crystalline semiconductors such as higher intensity of photoluminescence emission, better photoresponce and shift of band gap [H
In the anodic etching process, platinum is used as electrode, the GaN sample was connected by a copper wire to power supply and biased positive
It is believed that the concentration of holes through out the semiconductor surface area may be selective where holes may be more concentrated at certain area such as at the micro-defect area
Summary
GaN is one of the III-V compound semiconductors, where Ga is a trivalent element and N is a pentavalent element. The crystal structure of GaN can be in two types, wurtzite and zinc-blende crystal structure. The GaN sample used is the type of wurtzite structure, in the following, only wurtzite type of GaN will be discussed. Ga and N are bonded to each other by strongly covalent covalent bands. The covalent bonds are formed between tetrahedral “s1p3”- hybrid orbitals at the angles of “109.5 o”. The equation for the forming of covalent bonds of GaN may be written as following [Hartmut Haug et al (1993)]: Ga (4s24p1) + N (2s22p3) → Ga (4s14p3)+ + N (2s12p3)-
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