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Understanding of semiconductor breakdown under high electric fields is an important aspect of materials’ properties, particularly for the design of power devices. For decades, a power-law has been used to describe the dependence of material-specific critical electrical field ($${\mathcal{E}}_{\text{crit}}$$ E crit ) at which the material breaks down and bandgap (Eg). The relationship is often used to gauge tradeoffs of emerging materials whose properties haven’t yet been determined. Unfortunately, the reported dependencies of $${\mathcal{E}}_{\text{crit}}$$ E crit on Eg cover a surprisingly wide range in the literature. Moreover, $${\mathcal{E}}_{\text{crit}}$$ E crit is a function of material doping. Further, discrepancies arise in $${\mathcal{E}}_{\text{crit}}$$ E crit values owing to differences between punch-through and non-punch-through device structures. We report a new normalization procedure that enables comparison of critical electric field values across materials, doping, and different device types. An extensive examination of numerous references reveals that the dependence $${\mathcal{E}}_{\text{crit}}$$ E crit ∝ Eg1.83 best fits the most reliable and newest data for both direct and indirect semiconductors. Graphical abstract more...

We report the numerical study of n-GaN/i-InGaN/p-GaN solar cells on Ga-face substrates with thin GaN interlayers present in the intrinsic InGaN region. These interlayers have recently been shown to significantly increase the crystal quality of thick InGaN layers $$(>\!\!\!120\,\text{ nm})$$ . We find that tunneling is efficient in n-i-p structures having interlayers $$\le \! 1.5\,\text{ nm}$$ thick if polarization charges are sufficiently screened. If left unscreened, the large polarization charges naturally formed at the heterointerfaces degrades n-i-p performance, at a given interlayer thickness, because polarization charges increase the distance that carriers must tunnel. Simulations identify favorable parameter ranges. more...

We study n-GaN/i-InGaN/p-GaN solar cells on Ga-face substrates. We find that polarization charges at the heterointerfaces pin the value of VOC, JSC, and the fill factor to nearly optimal levels when the InGaN layer thickness exceeds a value dmin, even as the p- and n-layer thicknesses and doping concentrations vary widely. We verify an analytical approximation for dmin. We report nearly undiminished performance when an i-GaN setback layer is added between a p-doped layer and the i-InGaN layer - an addition that may be necessary to obtain good quality heterointerfaces. Additionally, the 2-D electron gas formed at the n-GaN/i-InGaN interface facilitates thinner n-GaN window layers for improved external quantum efficiency. more...

We study the use of a BGaN back-barrier layer in the GaN buffer of Al y Ga1 −y N/GaN highelectron mobility transistors to improve confinement of carriers in the 2D electron gas region. Unlike InGaN back-barrier designs, whose polarization-induced sheet charges form an electrostatic barrier at the backbarrier/ buffer interface, BGaN back-barrier designs create an electrostatic barrier at the channel/backbarrier interface. This can result in carrier confinement to sub-15 nm thickness, even when the channel is 30 nm wide. Although polarization sheet charges due to the BGaN back-barrier form a secondary well at the back-barrier/buffer interface, increasing the thickness of the back-barrier may move the secondary well so that it no longer interacts with the primary channel. more...

International audience; A GaN/ultrathin BGaN/GaN heterojunction is used in AlGaN/GaN high electron mobility transistors (HEMTs) to provide an electrostatic barrier to electrons and to improve the confinement of the 2-dimensional electron gas. BGaN back-barrier layers limit leakage in the GaN buffer thanks to two effects: a polarization-induced band discontinuity and a resistive barrier originating from excellent insulation properties of BGaN. Compared to conventional AlGaN/GaN HEMTs, structures grown with BGaN back-barrier showed a significant improvement of static performances, transport properties, and trapping effects involving a limited current collapse in dynamic regime. A DC maximum current increase of 58.7% was observed more...

In this paper we demonstrate a solution to systematically obtain thick, single phase InGaN epilayers by MOVPE. The solution consists in periodically inserting ultra-thin GaN interlayers during InGaN growth. Measurements by HAADF-STEM, X-ray diffraction, cathodoluminescence and photoluminescence demonstrate the effective suppression of the three-dimensional sublayer that is shown to spontaneously form in control InGaN epilayers grown without this method. Simulation predicts that tunneling through the GaN barriers is efficient and that carrier transport through this semi-bulk InGaN/GaN structure is similar to that of bulk InGaN. Such structures may be useful for improving the efficiency of InGaN solar cells by allowing thicker, higher quality InGaN absorption layers. more...

P-i-N structure solar cells often provide improved performance over N-i-P devices because acceptors are easier to activate when the p-type layer is close to the surface. However, for strained InGaN solar cells on GaN, the polarization-induced electric field creates a barrier for photocurrent that impedes device performance. In this paper we show that for Ga-face growth, N-i-P structures can provide improved performance because the electric field from the junction is parallel to that formed from polarization induced sheet charges. Thus the fields complement each other to assist in creating photocurrent in N-i-P devices. Additionally we simulate an N-i-P cell using the recently demonstrated insertion of ultra-thin GaN interlayers to achieve thick strained layers with high material quality. more...