Abstract

An increase of quantum yield under action of electron beam on the i-layer of GaN:Zn structure and KMgF₃ crystals have been observed(1,2). By means of the SEM we have been studied the plastic scintillators, CdS, ZnO and GaN:Zn-layers on the sapphire. Long time kinetic of the CL for all above materials was taken by the SEM “Stereoscan MK IIA” equipped by luminescent attachments. The CL contrast of direct writing patterns made by e-beam in the SEM was also analized. The fig.1 shows normalized depen­dences of CL intensity on the e-beam irradiation time under room temperature. The CL kinetic for plastic scintillators and CdS are described by curve 1. A possible mechanism of CL decreasing is a degradation of materials under local temperature action and defects creation that increases the concentration of nonradiative centers. A CL intensity variation for ZnO crystal did not observed(curve2). The curve 3 shows GaN:Zn -kinetic function for CL. The evolution of the CL was studied when an e-beam is fixed on a point of specimen. The increase of quantum yield and a very long life time of nonequilibrium state induced by e-beam are specific for last material. Such peculiarity allows by the SEM in CL mode to separate activated and nonactivated regions with contrast factor in the range of 30-100%. Above noted phenomena as result of e-beam action on media are non reversible and therefore the CL patterns by means of the SEM are available. Comparing the contrast(K) for three above cases one can seen that K= (I^ir-I^nir)/I^nir ≶ 0 (fig.2a,b), where I^ir is CL intensity of irradiated areas previousely, I^nir is CL intensity of nonirradiated areas previousely. The patterns on the plastic scintillators and CdS look like dark lines (K< 0) on the light field (fig.2a). The contrast patterns on ZnO crystals is absent (K=0). In this case the e-beam action effect is reversible with relaxation time smaller than 10⁻⁶s. For GaN:Zn layer K>0 (fig. 2b) and when I^ir attains a maximum the K-value can reach the factor of loo. Besides the previousely irradiation areas of GaN:Zn-layer having Iir ≫ I^nir keep the contrast under room temperature up to date more 24 month(for T=0–10°C over 10 year). Minimum sizes of luminescent patterns elements (lines, spots) are equal to 0,5-0,6 mkm. Patterns do not change own geometry in time. The limit of spatial resolution is determined by the volume occupied by scattered electrons of the primary beam. The direct writing and reading information by e-beam are available with digital and analogue modes. Writing density is over 10⁸ bit/cm². No change in the luminescent spectrum of GaN:Zn before and after e-beam action on layers was detected. The CL intensity is only varied. We suggest that the luminescence changes vs the irradiation time are due to possible generation of new radiative recombination centers in the volume.

© 1984 Optical Society of America