Optical absorption on localized levels in gallium arsenide

Abstract

The extrinsic optical absorption associated with defects in G~has been studied between 4 and 300'K in the range from 0.6 to 1.5 eV. Two bands in particular are investigated: the first located around 0.9 eV is associated with chromium; the second at 1.2 eV, present in all materials, is probably related to some native defects such as galhum vacancies. The variations of the energy and of the shape of these two bands versus temperature demonstrate that they cannot come from transitions between extrinsic levels and the energy bands of the perfect crystal. The absorption curves of each line appear to be Gaussian at every temperature. As a consequence of lattice coupling, the width of these bands increases greatly with temperature according to a law: W'(T) = 8'(0) fcoth(h vg/2k T)]'". Finally, it is sho~n that a configurational-coordinate diagram may be applied to these two centers. On this basis, we give the values of the quantum energy of vibration of the centers in their ground states h vg: 13 meV for the chromium center, and 15 meV for the center at 1.2 eV. For this last one, we propose a configurational~rdinate diagram assuming the parabolic approximation to be valid. These results are discussed and compared with those obtained by photoconductivity or photoluminescence in GaAs, taking into account the important Stokes shift resulting from the lattice coupling we mentionned above.In particular, it is shown that the center absorbing at 1.2 eV is quite difFerent of that emitting at 1.2 eV, i.e., the Vo, :D complex for which %'illiams has already proposed a configurational-coordinate diagram.

Strain‐Associated Band Tailing Effect in Semiconductors

“…2 shows the optical absorption edge of a bulk chromium doped GaAs sample. The residual absorption visible on the low energy side of the curve is due to transitions involving deep levels [12]. If this absorption is subtracted, one gets a curve which can be fitted to the theoretical law [4].…”

Interpretation of luminescence in GaAs : Cr : 0.839 eV and 0.574 eV lines

“…In absorption, a transition has been related to the photoionization Cr3 + + electron in the valence band -Cr2+ [14]. As said above, a band at 0.9 eV [10] with its zero-phonon line at 0.820 eV [45] corresponds to the internal transition in the Cr2+ ion. The 0.9 eV absorption band is observed in n-type Cr-doped samples, as well as the 0.61 eV band is in ' luminescence.…”

“…sistors, logical circuits) as well as the difficulties encountered in its use both as epitaxial substrate and as implantation substrate have led to a lot of studies related to that material. Optical spectroscopic measu.. rements (photo and cathodoluminescence [1][2][3][4][5][6][7][8][9], absorption [10][11][12][13][14], D.L.O.S. [15]), magnetic studies [16][17][18][19][20][21][22][23] as well as electrical measurements (D.L.T.S.…”

YAG photoluminescence of GaAs : Cr

“…We can also explain in that model why the internal transition (5E-5T2) in Cr2+ should not be seen. The 5 E state is degenerated with the conduction band [16,17] and therefore, the transition to the Cr2+ level are more probable from the bottom of the conduction band. The DLTS results [18] are also in reasonable agreement with the thermal values given by our model.…”