PLANAR-DOPED-BARRIER DIODE

The planar-doped-barrier (PDB) diode is often called the cS-doped-barrier diode or triangular-barrier diode, due to the shape of the potential barrier. It belongs to a class of bulk-barrier diodes which are different from the most common majority-carrier device, the Schottky-barrier diode whose barrier is formed at the semiconductor surface. The development that led to this device started from the idea of enhancing the Schottky-barrier height by a thin, depleted region of high concentration of the opposite type at the surface, proposed by Shannon in 1974. Shannon, later in 1979, developed a new majority-carrier device called a camel diode in which the metal-semiconductor barrier was eliminated and the barrier was created by an n++-p+-n structure. The planar-doped barrier was first reported by Malik et al. in 1980. The structure differs from the camel diode by having layers of intrinsic regions inserted between the oppositely doped layers, i.e., n+-i-p+-i-n structure.

A typical planar-doped-barrier diode is in GaAs. Because the middle p+-layer has to be fully depleted, it is very thin and it lies in the range of 2-10 nm. Such a thin, heavily doped layer can only be controlled by MBE or MOCVD growth. Besides, thermal cycles during subsequent processing have to be constrained to avoid excessive diffusion. The doping level is typically in the 1018 cm-3 range. The intrinsic regions range from tens of nm to several hundred nm, and have concentrations in the 1014 cm 3 range. The mesa structure can be obtained by etch-back of the planar epitaxial layers.