Doping limits in semiconductors are discussed in terms of the amphoteric defect model (ADM). It is shown that the maximum free electron or hole concentration that can be achieved by doping is an intrinsic property of a given semiconductor and is fully determined by the location of the semiconductor band edges with respect to a common energy reference, the Fermi level stabilization energy. The ADM provides a simple phenomenological rule that explains experimentally observed trends in free carrier saturation in a variety of semiconductor materials and their alloys. The predictions of a large enhancement of the maximum electron concentration in III–N–V alloys have been recently confirmed by experiment.

Intrinsic limitations to the doping of wide-gap semiconductors

Doping of III-V semiconductors is an essential part of growth and processing technology for optoelectronic and high speed electronic devices. This review covers several recent developments in III-V doping including (i) the high-concentration regime for p-type dopants in InP and GaAs, (ii) the sensitivity of doping incorporation on the crystal orientation, (iii) compensation mechanisms in Si-doped GaAs, and (iv) p-type carbon doping in GaAs and AlxGa1-xAs.

Doping in III-V Semiconductors

The reverse leakage current of a GaInN light-emitting diode (LED) is analyzed by temperature dependent current–voltage measurements. At low temperature, the leakage current is attributed to variable-range-hopping conduction. At high temperature, the leakage current is explained by a thermally assisted multi-step tunneling model. The thermal activation energies (95–162 meV), extracted from the Arrhenius plot in the high-temperature range, indicate a thermally activated tunneling process. Additional room temperature capacitance–voltage measurements are performed to obtain information on the depletion width and doping concentration of the LED.

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Transport-mechanism analysis of the reverse leakage current in GaInN light-emitting diodes

A review of InP/InAlAs/InGaAs based transistors for high frequency applications

Spatial localization of Be in δ‐doped GaAs within few lattice constants (<20 A) is achieved at low growth temperatures for concentrations N2DBe <1014 cm−2 as indicated by capacitance‐voltage profiles and secondary ion mass spectroscopy. At elevated growth temperatures and at higher Be concentrations, significant spreading of the dopants occurs and is explained by (i) Fermi‐level pinning‐induced segregation, (ii) repulsive Coulomb interaction of dopants, and (iii) diffusion. The highest Be concentration achieved at low growth temperatures exceeds 2×1020 cm−3 and is limited by repulsive dopant interaction. It is shown that the repulsive Coulomb interaction results in a correlated, nonrandom dopant distribution. The diffusion coefficient of Be in GaAs is determined and is found to be much lower than previously reported.

Beryllium δ doping of GaAs grown by molecular beam epitaxy

The study of diffusion and drift of Si in AlxGa1−xAs by means of capacitance‐voltage measurements reveals that low substrate temperatures during growth by molecular beam epitaxy are required to achieve δ‐function‐like doping profiles. The diffusion coefficient of Si in Al0.3Ga0.7As is determined. We further show theoretically that the random Poisson distribution (usually assumed for dopant distributions in semiconductors) should be modified at high dopant concentrations due to repulsive interactions of impurities.

Diffusion and drift of Si dopants in δ‐doped n‐type AlxGa1−xAs

The spatial resolution of the capacitance‐voltage profiling technique on semiconductors with one‐dimensional quantum confinement is shown to be given by the spatial extent of the wave function. The Debye length limitation does not apply. Capacitance‐voltage profiles on δ‐doped GaAs of density 4–4.5×1012 cm−2 exhibit widths of 20 and 48 A for p‐ and n‐type impurities, respectively. The profiles agree with the theoretical resolution function and with Be and Si profiles measured by secondary‐ion mass spectroscopy. It is further shown that the saturation of the free‐carrier density of highly Si δ‐doped GaAs grown by molecular beam epitaxy is due to inactive Si impurities

Spatial resolution of the capacitance‐voltage profiling technique on semiconductors with quantum confinement

Improved resolution of secondary‐ion mass spectrometry (SIMS) is obtained on Be δ‐doped GaAs grown by molecular beam epitaxy at a temperature of 500 °C. The measured impurity distribution width is 29 A, which corresponds to a SIMS resolution of ΔzR=25 A. Impurity diffusion lengths of ≤10 A can be detected by the technique. The surface segregation of Si impurities in δ‐doped GaAs grown at 660 °C is investigated as a function of doping density. The segregation length increases with the Si density and is consistent with a segregation model based on the pinning of the Fermi level at the growing GaAs surface.

J. M. Kuo

Papers

Beryllium δ doping of GaAs grown by molecular beam epitaxy

Diffusion and drift of Si dopants in δ‐doped n‐type AlxGa1−xAs

Spatial resolution of the capacitance‐voltage profiling technique on semiconductors with quantum confinement

Secondary‐ion mass spectrometry on δ‐doped GaAs grown by molecular beam epitaxy