Time resolved photoluminescence study of Si modulation doped GaN/Al_0.07Ga_0.93N multiple quantum wells

Abstract

The effects of the Si doping level on the recombination dynamics and carrier (exciton) localization in modulation doped GaN/Al 0.07 Ga 0.93 N multiple-quantum-well (MQW) structures were studied by means of photoluminescence (PL) and time-resolved PL measurements. All samples with different doping levels show a QW emission which is blue shifted with respect to the 3.48 eV PL peak from the GaN buffer layer. The decay time at the peak position remains nearly constant in the range of 320-420 ps at 2 K for all doping levels. For the undoped and low-doped samples (3 × 10 18 cm -3 ), which have less free electrons in the QWs, a non-exponential PL decay behaviour at 2 K is attributed to localized exciton recombination. The more highly doped samples (5 × 10 18 cm -3 to 10 20 cm -3) show almost exponential decay curves at 2 K, suggesting the recombination of free electrons and localized holes. This localization effect appears even at high electron concentrations to cancel the expected lowering of the radiative lifetime with doping at 2 K; such a lowering is clearly observed at elevated temperatures for the highly doped samples, however. The internal polarization-induced fields of the medium and highly-doped samples are partly screened by the electrons originating from the doping in the barriers. Only the PL peak of the undoped and low-doped samples shows a redshift with time delay, related to the photogenerated carriers.

Radiative recombination mechanism in highly modulation doped GaN/AlGaN multiple quantum wells

“…1). Time-resolved PL measurements [7] have revealed that the decay time is nearly independent on the emission energy and has a value of 350-400 ps in all doped samples. This is quite surprising for modulation doped QWs and could only be explained if localized holes are involved in the optical transitions.…”

“…Moreover, a degenerate two-dimensional (2D) electron gas is formed in the wells and many-body effects have to be considered in the analysis of the recombination mechanism. Recently, we have studied in detail the low-temperature emission in shallow GaN/AlGaN multiple quantum wells (MQWs) with heavily Si-doped barriers [6,7]. An asymmetrical emission lineshape with the peak energy exhibiting a nonmonotonic dependence on the doping density has been observed.…”

Observation of hot luminescence and slow inter-sub-band relaxation in Si-doped GaN∕AlxGa1−xN (x=0.11, 0.25) multi-quantum-well structures

“…42,43 In general, Si doping improves the radiative efficiency due to screening of the well-width fluctuations and partial compensation of the electric field. 40,44,45 In this work we first analyze the structural quality of GaN / AlGaN MQW structures grown by PAMBE under different conditions. The sample structure was designed for ISB transitions in the mid-infrared, i.e., below the LO-phonon energy.…”

Experimental and theoretical investigations of optical properties of GaN/AlGaN MQW nanostructures. Impact of built-in polarization fields

“…These polarization charges create internal fields in the QWs of the order of MV/cm which have fundamental influence on the optical properties and strongly affecting the oscillator strengths of excitons as well as the spectral position of the correspon− ding photoluminescence (PL) peaks. A huge redshift of the transition energy and a strong increase in the carrier lifetime due to the quantum confined Stark effect are marked fea− tures in the optical spectra of GaN/AlGaN quantum wells, extensively debated in many publications [9,10].…”