Influence of the roughness of molybdenum back electrode on the photodiode characteristics under He–Ne illumination

Abstract

Molybdenum thin films, about 300 nm thick, were RF sputtered on silicon wafers used as a substrate, in order to produce thin film diode back electrodes. The Mo films were treated with reactive ion etching (RIE) for different times (20 s, 40 s, 60 s and 120 s), producing surfaces with different degrees of roughness. Atomic force microscopy (AFM) showed a pyramidal structure of the etched surfaces. It was found that the roughness is strongly related to the RIE time. The change of the reflection coefficient of the etched Mo surfaces was measured with respect to the non-etched (as-is) Mo surface. The results showed dependence of the relative change of the surface reflection with the RIE time. Such prepared molybdenum surfaces of different roughness were used as back electrodes for preparation of hydrogenated amorphous silicon p-i-n diodes, prepared by the plasma-enhanced chemical vapour deposition method (PECVD). Molybdenum coating (150 nm thick) by RF sputtering was also used to produce top electrodes. The final diode structure was Mo/p-i-n/Mo. The grid structure of the top electrode was produced by a photolithography technique. Thirteen various front electrode grid patterns were designed to permit the He-Ne laser beam spot of 7 mW and about 0.7 mm cross-section. The laser beam penetrated through the p-i-n structure, covering the entire diode active area. The short circuit current (I sc ) was measured for 13 diode grid shapes of each sample, including the diodes on the flat (untreated) back Mo electrode. The results showed that the average I sc depends on the RIE time. The dark and He-Ne light characteristics showed changes with the RIE time. From the measured IV characteristics, the serial resistance (R s ) was found to increase with the RIE time, except for the 20 s treated RIE sample. Results of I sc and R s suggested that, besides the light scattering mechanism resulting from the surface roughness, there is another contributing factor to the photodiode performance enhancement, and that is the surface of the pi junction; the greater the roughness, the larger the junction area.

Structural, optical, vibrational and photoluminescence studies of Sn-doped MoO 3 sprayed thin films

“…On the other hand, the texture coefficient (TC) which indicates the maximum preferred orientation of the films along the diffraction plane means that the increase in the preferred orientation is associated with the increase of the number of grains along that plane. TC(h k l) values have been calculated from X-ray data, using the following formula [30,33,35,36] XRD spectra were used to study the effect of incorporation of the element Sn in the MoO 3 matrix respectively on the crystallite size, using the formula Deby-Scherrer [37][38], the stress [39] and dislocation density [30,37] 1 D…”

Optical, Physical, Chemical and Electrical Properties of Nickel Oxide Sprayed Thin Films under Tin Doping Effects

“…Figure 4 shows 3D topography performed with Atomic Force Microscope of tin doped NiO thin films. The root mean square roughness (Rq) values were obtained from AFM observations and calculated using the following relation [41]:…”

Structural, opto-thermal and electrical properties of ZnO:Mo sprayed thin films

“…In the same line, the root mean square roughness (R q ) is calculated by the following relation [41]:…”