Decay behaviour of high‐excitation luminescence in GaP:N. I. Model for the decay of two coexisting phases

Abstract

The time behaviour of the radiative recombination of nitrogen-doped GaP is investigated a t pulsed intense optical excitations and low temperatures (2' = 2 and 27 K). The decay behaviour of the luminescence intensities corresponding to the electron-hole liquid (EHL) and the coexisting lowdensity phase (LDP) is found for all nitrogen concentrations (nN = 2 x 10'' to 2.9 x 10'8 ~3 1 1~~) to be nonexponential. It is interpreted as a consequence of interactions between both coexisting phases. A model is introduced where the EHL is fed by the LDP continuously. It describes the observed decay of the luminescence very well, even for different nitrogen concentrations and different excitation intensities.Es wird das Zeitverhalten der strahlenden Rekombination von stickstoffdotiertern GaP unter intensiver optischer Impulsanregung bei T = 2 und 27 K untersucht. Das Abklingverhalten der Lumineszenzintensititen, die der Elektron-Loch-Fliissigkeit (EHL) sowie der koexistierenden Niederdichtephase (LDP) entsprechen, ist fur alle hier untersuchten Stickstoffkonzentrationen (TLN = 2 x 10'' bis 2,9 x 10l8 nichtexponentiell. Es wird als Folge der Wechselwirkungen zwischen beiden koexistierenden Phasen angesehen. Ein entsprechendes Modell wird vorgeschlagen, wobei die EHL laufend von der LDP aufgefiillt wird. Es beschreibt das Abklingverhalten der Lumineszenz beider koexistierenden Phasen fur unterschiedliche Stickstoffkonzentrationen nnd Anregungsintensitaten sehr gut.

On the Bleaching of the A‐Bound Exciton Absorption in GaP: N. An Example for an Electron–Hole Liquid Induced Optical Nonlinearity

“…Single-beam transmission vs. incident peak intensity for hw = E,. Dots experimental points, dashed line calculated for the two-level saturation (8) and (9), full line calculated for the electron-hole liquid model (19) and (20)…”

“…Dots experimental points, dashed line calculated for the two-level saturation (8) and (9), full line calculated for the electron-hole liquid model (19) and ( is so large, that interaction processes between bound excitons a t different centres are of no importance (?i0& < 0.01 with a,, being the bound exciton radius). Therefore, the system is ideally two-level like.…”

“…The steady-state nonlinear absorption characteristic originating from this process is simply obtained from (12) and (19) setting dxldt = 0. Though the underlying mechanism is completely different, the result is formally equivalent with that for two-level systems (22), but with a cw saturation intensity given now by The analysis in Section 4.2 has yielded that for neq the corresponding value of the "lowdensity" phase has t o be used.…”

“…As for above-gap excitation the broad emission band related to the liquid appears simultaneously with the input pulse. Because bound excitons do not exist in the droplets we have instead of (15) a t resonant excitation or in terms of the filling factor only (19) dx -(1 -~) a o I o -2 _ _ dt fzwneq ZD 3, One of the currently discussed models of the binding of an exciton a t the isolated N impurity [17] is, that t i t first the electron is captured by the short-ranged potential of the neutral impuiity and then the resulting Coulomb potential binds the hole. In this case the bound exciton becomes very similar to an acceptor state.…”

“…We have solved (19) inserting (10) for the input pulse and neq = 5 x 101s cm-3 as well as using zD = 28 ns, which has been deduced in [19] for the carrier lifetime in the low-density phase. Knowing x(t) we have then calculated similar to (9) the nonlinear transmission change according to our experimental arrangement For the nitrogen concentration (2 x 10l8…”