Optical and Electrical Characterisation Study of SiCl₄ Reactive Ion Etched Gaas

Abstract

In this study 10¹⁶cm^-3 n-type epitaxial GaAs was reactive-ion-etched (RIE) in a parallel plate type reactor as a function of rf power and gas pressure using a SiCl₄ plasma. The sample matrix followed a 3 level 3 factorial statistical experimental design. Photoreflectance (PR) was employed to characterise the etch induced modification to the electronic band structure at the fundamental band-edge transition. Variable angle spectroscopic ellipsometry (VASE) and photoluminescence (PL) optical diagnostic techniques are also employed to characterise the plasma processed GaAs. PR results detail a decrease in the surface electric field (F_s) with etch severity arising from an RIE induced electron trap that increases in concentration with energetic ion sputtering. For the highest rf power densities PR further distinguishes between reactant desorption and adsorption limited etching regimes. VASE and PL data reveal the extent and degree of surface modification of the etched substrates. Atomic-Force-Microscopy showed the etched surfaces to have an average roughness, R_a of 15nm. Optical characterisation data are correlated with electrical measurements using fabricated Schottky barrier diodes for deep-level-transient spectroscopy (DLTS) as well as current-voltage and capacitance-voltage (CV) analysis. CV results detail a reduced surface carrier concentration after RIE while DLTS revealed the emergence of six electron trap defect levels. One of the two prominent RIE induced trap levels exhibited similar DLTS behaviour as that produced after ion bombardment of n-type (Si) GaAs.