holedoping

Hole doping is the deliberate introduction of positive charge carriers, or holes, into a material to modify its electrical properties. In semiconductors and related materials, holes arise when electrons are removed from the valence band or from an impurity level, leaving behind vacancies that can move through the lattice as charge carriers. Holes carry positive charge and often behave as the majority carriers in p-type materials, in contrast to electron-doped or n-type materials where electrons are dominant.

Doping methods and examples. In elemental semiconductors such as silicon, acceptor impurities like boron substitute for silicon atoms and accept electrons, creating holes that participate in conduction. In III–V semiconductors, elements such as aluminum or zinc can serve as acceptors. In complex oxides and high-temperature superconductors, hole doping is commonly achieved by substituting divalent ions for trivalent ones (for example, Sr2+ for La3+ in certain cuprates) or by adjusting oxygen content to modify the oxidation state and hole concentration in the CuO2 or related planes.

Effects and characterization. The concentration of holes determines the material’s conductivity, mobility, and Fermi level position. The Hall coefficient and Seebeck coefficient help identify the type and density of the majority carriers, with positive Seebeck coefficients indicating hole conduction. In many materials, increasing hole doping can drive a transition from insulating to metallic behavior and, in some layered oxides such as cuprates, can induce superconductivity within a dome-shaped doping range.

Applications and challenges. Hole-doped semiconductors are essential for p-type devices, including diodes, transistors, and certain solar cells. They are also used in thermoelectric materials where carrier concentration optimization enhances performance. Controlling hole concentration can be challenging due to defect compensation, diffusion during processing, and sensitivity to stoichiometry and temperature.