Introducing the spiked p-n junction for tunnel devices and current gain

By serendipity, a novel feature has appeared in regrown GaN p-n junctions. When the device is exposed to atmosphere in between the growth of the n and p regions, a sheet layer of donors (primarily oxygen) incorporates at the junction interface [1,2]. This has been argued to decrease the depletion width, which boosts tunneling currents to acceptable levels for contacts to GaN LEDs [1]. While this is useful in its own right, a general analysis of the electrostatics of a sheet charge in a p-n junction yields another interesting regime not yet reported. Given sufficiently large interface charge, the n-side may enter accumulation, forcing a “spike” into an otherwise typical homojunction p-n band diagram. Such spikes may prove relevant for the design of tunnel junctions, or for homojunction gain elements (similar to the delta-doped BJTs of [3]).