Anomalous PL brightening caused by impact formation of a (D ⁺ , X) complex during an impact ionization avalanche in n‐GaAs

Abstract

The impact formation of the (D + , X) bound-exciton in n-GaAs at 4.2 K during an impact ionization avalanche under an applied pulse voltage has been investigated. The bright PL-pattern observed by applying the pulse voltage characterizes well the formation of a current density filament. The observations of the bright PL-pattern give a quite new result concerning the electron-impact formation process of the excitons bound to the ionized donors (D + , X).At low temperatures, high-purity semiconductors behave like insulators, because a large part of the shallow impurities is charge-neutral and only a few charge carriers can be mobile. By applying an electric field of a few V/cm, the neutral shallow impurities are completely ionized due to an impact ionization avalanche, causing the negative differential resistivity (NDR) in the current−voltage characteristic. By the low-temperature impurity breakdown, a current density filament can be formed between the ohmic contacts [1, 2]. The current density filament has been typically observed as a photoluminescence (PL) quench-pattern [3].By the PL method, Aoki and Fukui [4−6] have investigated the nucleation process of a current density filament [4] and also the nonlinear dynamics of the filament during the current instability under magnetic fields in n-GaAs [1,5,6]. Very recently, the author has found, that the PL pattern image under a short pulse voltage can be seen as a bright pattern inside the filament or along the filament boundaries in a n-GaAs Corbino disc [7,8], where the anomalous brightening of the PL intensity was seen under a very weak photoexcitation density. In this paper, the anomalous PL brightening during the impact ionization avalanche of the neutral shallow donors is discussed in detail, and a new interpretation of the impact formation of the excitons bound to ionized donors is given.All of the measurements were done at 4.2 K, using a high-purity n-GaAs sample with a thickness of the epitaxial layer of 21 µm grown on a semi-insulating substrate. The electron density and the electron mobility were n = 6.23 × 10 13 cm −3 and µ = 1.23 × 10 5 cm 2 /Vs at 77 K, respectively. The area of the sample surface was approximately (6.0 × 6.0) mm 2 , on which the disk-shaped ohmic contacts were formed (see Fig. 1). The sample surface was very weakly excited by a 35 mW (or 20 mW) He−Ne laser beam, where the laser beam was spread over the whole sample surface by using a spatial filter and strongly attenuated by using neutral density filters. The photon density was J p ≈ 63 µW/cm 2 . The spatiotemporal

Anomalous PL brightening caused by partial Auger recombination of a (D0, X) complex during an impact ionization avalanche in n-GaAs

“…In Refs. [9,10], we have not measured the photoluminescence spectra under the weak photoexcitation density. By setting a grating monochromator between the cryostat (sample) and the image intensifier, the PL spectra were resolved under the weak photoexcitation only with the bad S/N ratio.…”

“…3-5, where wZ2.3 ms, w t Z2.0 ms and t d Z255 ns. For the origin of the bright filament, previously we have missread and concluded [9,10] that the impact formation of the (D C , X) complex is responsible for the PL brightening. In Refs.…”

“…Very recently, Aoki has found, that the PL pattern image under a short pulse voltage can be seen as a bright pattern inside the filament or along filament boundaries in a n-GaAs Corbino disc [7,8] and also in disk shaped contacts [9,10], where the anomalous PL brightening of the PL intensity has been seen under a very weak photoexcitation density. In this paper, the PL spectra related to the PL brightening inside the current density filament are discussed in detail, and an interpretation of the partial Auger recombination process of the (D 0 , X) complex [11,12] is given.…”

“…lengthen (wz10 ms), the pattern image of the current density filament is quenched. The quenched PL pattern observed with wz10 ms has been found to be caused by the joule heat due to the pulse current as well as by the impact ionization of the neutral donors [7][8][9][10].…”