ELECTRON-DISTRIBUTION AND CAPACITANCE-VOLTAGE CHARACTERISTICS OF N-DOPED QUANTUM-WELLS

The effect of multiple quantum well (MQW) parameters on the free carri er distribution (FCD) and the apparent carrier distribution (ACD) obta ined from capacitance-voltage (C-V) profiling has been investigated us ing a self-consistent simulation technique and the C-V profiling techn ique. The FCD in MQW structures reveals large outer peaks and small in ner peaks even when all the parameters of each quantum wells (QWs) are the same. Such a feature becomes more apparent as the barrier layer b ecomes thinner or the barrier doping level becomes lower. These charac teristics are found to originate from the fact that the density of car riers confined in each well is mostly determined by the depletion regi on formed alongside the well via the charge neutrality condition. The ACD is found to vary drastically as the thickness or the doping level of barrier changes. When the Debye averaging process is prominent, the ACD peaks are broader and smaller than the FCD peaks and are displace d toward the bottom layer side. The ACD inner peaks even disappear com pletely when the Debye screening length is comparable to or larger tha n the QW period, while real free carriers are well confined in each we ll. The effect of temperature on the UCD through the Debye averaging p rocess is also investigated. When the Debye length is much smaller tha n the QW period, the full width at half maximum of the ACD is determin ed by the change of the position expectation value of the two-dimensio nal differential carriers. This change of position expectation value i s found to be much smaller than the well width for relatively narrow Q Ws. The accuracy of our simulation results is confirmed by the excelle nt agreements between the simulated ACDs and the measured ACDs of In0. 2Ga0.8As/GaAs MQWs. As an example of extracting the qualitative inform ations from the measured C-V profile, the C-V profiles of partially st rain relaxed InxGa1-xAs/GaAs MQWs with x=0.15 and x=0.25, grown by met al organic chemical vapor deposition, are discussed. These results sho w systematically how the QW parameters affect the FCD and the ACD. (C) 1998 American Institute of Physics. [S0021-8979(98)05627-8].