Superinjection of Holes in Homojunction Diodes Based on Wide-Bandgap Semiconductors

Abstract

Electrically driven light sources are essential in a wide range of applications, from indication and display technologies to high-speed data communication and quantum information processing. Wide-bandgap semiconductors promise to advance solid-state lighting by delivering novel light sources. However, electrical pumping of these devices is still a challenging problem. Many wide-bandgap semiconductor materials, such as SiC, GaN, AlN, ZnS, and Ga₂O₃, can be easily n-type doped, but their efficient p-type doping is extremely difficult. The lack of holes due to the high activation energy of acceptors greatly limits the performance and practical applicability of wide-bandgap semiconductor devices. Here, we study a novel effect which allows homojunction semiconductor devices, such as p-i-n diodes, to operate well above the limit imposed by doping of the p-type material. Using a rigorous numerical approach, we show that the density of injected holes can exceed the density of holes in the p-type injection layer by up to four orders of magnitude depending on the semiconductor material, dopant, and temperature, which gives the possibility to significantly overcome the doping problem. We present a clear physical explanation of this unexpected feature of wide-bandgap semiconductor p-i-n diodes and closely examine it in 4H-SiC, 3C-SiC, AlN, and ZnS structures. The predicted effect can be exploited to develop bright-light-emitting devices, especially electrically driven nonclassical light sources based on color centers in SiC, AlN, ZnO, and other wide-bandgap semiconductors.

Keywords: aluminum nitride; light-emitting diodes; silicon carbide; single-photon sources; superinjection in homojunction diodes; zinc sulfide.

Figure 1

(a,b) Schematic illustration of electron and hole injection in a forward biased double heterostructure (a) and qualitative distribution of electron density (b). (c,d) Illustration of electron injection in a diamond p-i-n diode at a high forward bias voltage (c), and spatial distribution of electrons under these conditions (d).

Figure 2

(a) Schematic illustration of the 4H-SiC p-i-n diode: d = 5 μm; all parameters of the diode used in the simulations can be found in the Supplementary Material. (b) Electrostatic potential profile at different bias voltages. (c) Spatial distribution of electrons in the diode at different bias voltages. (d,e) Spatial distribution of holes in logarithmic (d) and linear (e) scales at different bias voltages. (f) Spatial map of the hole current and its components in the diode at V = 4.0 V (J = 380 A/cm²).

Figure 3

Dependence of the maximum hole density in the i-region of the 4H-SiC p-i-n diode on the injection current for different donor concentrations in the n-type injection layer. The 50 nm-thick areas near the p–i and i–n junctions are ignored to avoid overestimation of the density of injected holes.

Figure 4

(a) Dependence of the hole density in the p-type injection layer on the acceptor ionization energy. The acceptor compensation ratio is equal to 5%. (b) Dependence of the maximum hole density in the i-region of the 4H-SiC p-i-n diode, which is normalized to the density of holes in the p-type layer p_eqp, on the injection current for different activation energies of acceptors in the p-type injection layer. The 50 nm-thick areas near the p–i and i–n junctions are ignored to avoid overestimation of the density of injected holes. (c) Spatial distribution of holes in the 4H-SiC p-i-n diode for different activation energies of acceptors in the p-type injection layer at an injection current density of 200 A/cm². The hole density is normalized to the density of holes in the p-type injection layer. (d) Variation of the spatial distribution of holes in the 4H-SiC p-i-n diode with the activation energy of acceptors in the p-type injection layer at an injection current density of 200 A/cm². The hole density is normalized to the density of holes in the p-type injection layer.

Figure 5

(a) Electron density in the n-type layer and hole density in the p-type layer as functions of temperature. (b) Dependence of the maximum hole density in the i-region of the 4H-SiC p-i-n diode on the injection current for three different temperatures and two different activation energies of acceptors. The 50 nm-thick areas near the p–i and i–n junctions are ignored to avoid overestimation of the density of injected holes. The material parameters of 4H-SiC at 200 K and 400 K are provided in the Supplementary Material.

Figure 6

(a–c) Spatial distribution of the hole density in the i-region of the three p-i-n diodes based on 3C-SiC with the p-layer doped with gallium (a), AlN (b), and ZnS (c). The hole density is normalized to the hole density in the p-type layer. (d) Dependence of the maximum hole density in the i-region of different the p-i-n diodes. The 50 nm-thick areas near the p–i and i–n junctions are ignored to avoid overestimation of the density of injected holes. The hole density is normalized to the density of holes in the p-type injection layer. For the 3C-SiC diode, two dopants (Al and Ga) of the p-type layer are considered. The parameters of the 3C-SiC, ZnS, and AlN diodes are listed in the Supplementary Material.