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Impact ionisation electroluminescence in planar GaAs-based heterostructure Gunn diodes: Spatial distribution and impact of doping non-uniformities
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) Representative EL image from a 4 μm-long and 60 μm-wide Gunn diode biased at 8 V, overlaid on a white light image of the device. White arrows indicate the location from where the EL intensity profile of Figure 2(b) is extracted. (b) Schematic of the Gunn diodes analysed in this work.

Image of FIG. 2.
FIG. 2.

(a) Representative EL spectrum from a 2 μm-long and 60 μm-wide device biased at 4.5 V. The equivalent electron temperature is extracted from a fit to the high energy tail as indicated with the dotted line. (b) Longitudinal profile of EL intensity from Figure 1(a) along the line delimited by the white arrows. The vertical dash-dotted lines indicate the cathode and anode contacts. (c) EL intensity profiles obtained from the image in Figure 1(a) along lines parallel to the contacts, starting at the cathode edge, and in 0.5 μm steps, offset for clarity. The two vertical dotted lines at the left and right sides of the figure indicate the lateral limits of the device mesa.

Image of FIG. 3.
FIG. 3.

Top view Monte Carlo simulations of a planar Gunn device. (a) Evolution of the Gunn domains in a 7 μm-wide and 1.4 μm-long Gunn device biased at 6 V. Black dots, indicating electron particle positions, show a domain in transit. The two high electron density vertical stripes on the left and right ends are the cathode and anode ohmic contacts, respectively. Doping in the transit and contact regions was 1 × 1017 and 1 × 1018 cm−3, respectively. (b) Similar model as in (a) but with a higher electron density region (2 × 1018 cm−3) placed on the anode contact. The two parallel horizontal lines are a guide to the eye indicating the region of the device just in front of the doping inhomogeneity. (c) The density product of electrons and holes in the transit region, averaged over several Gunn domain transit periods, showing enhancement in the central region due to increased hole production in the higher density contact. Typical electron and hole densities are 1017 and 1016 cm−3, respectively. The step in electron-hole density product between consecutive contours is 1 × 1033 cm−6.

Image of FIG. 4.
FIG. 4.

(a), (b), and (c), show the electric field in a 3 μm-long device under 7 V bias at several instants during the transit of a Gunn domain. (a) One domain leaves the device, showing a maximum field of 300 kV cm−1, whereas a new one forms at the cathode. (b) Same device 7 ps later, with the new domain progressing towards the anode. (c) After another 7 ps the domain has progressed further towards the anode and the field strength is becoming strong enough to cause some impact ionisation. (d) Impact ionisation event locations over the transit of a domain

Image of FIG. 5.
FIG. 5.

Electron (left column) and hole (right column) densities in a longitudinal section of a 1.4 μm-long device operating at 6 V. (a) Domain about half way through the cycle with a high density of holes still under and close to the anode. (b) As the domain approaches the anode, the increasing field depletes the anode region of holes. (c) A newly forming domain with the old domain still passing out of the anode together with a new crop of holes next to the anode.

Image of FIG. 6.
FIG. 6.

(a) Device schematic showing the lines along which the electron and hole density profiles of (b) and (c) are taken. (b) Electron (−) and hole (+) densities in the horizontal direction along the red AB line of (a). The location of the cathode and anode contact edges is indicated. (c) Electron (−) and hole (+) densities in the vertical direction along the blue CD line of (a). The dotted arrows indicate the location of the AlGaAs barrier layers. In (b) and (c), both the electron and hole densities are averaged over the transit of several Gunn domains and are shown as the log10 of ρ, the density in cm−3.

Image of FIG. 7.
FIG. 7.

(a) Electron-hole density product in a longitudinal section of the device, averaged over the transit of several Gunn domains. The scale is the same as in Figure 3(c) . (b) Detail of an EL image from a representative 2 μm-long device biased at 6.5 V. (c) Longitudinal EL intensity profile from (b) at the location indicated by the arrows. The EL intensity at each point was integrated over the width indicated by the two parallel lines in (b). The vertical dashed lines indicate the location of the contact edges.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Impact ionisation electroluminescence in planar GaAs-based heterostructure Gunn diodes: Spatial distribution and impact of doping non-uniformities