Photoconductivity and photoluminescence under bias in GaInNAs/GaAs MQW p-i-n structures
© khalil et al.; licensee Springer. 2012
Received: 10 July 2012
Accepted: 12 September 2012
Published: 28 September 2012
The low temperature photoluminescence under bias (PLb) and the photoconductivity (PC) of a p-i-n GaInNAs/GaAs multiple quantum well sample have been investigated. Under optical excitation with photons of energy greater than the GaAs bandgap, PC and PLb results show a number of step-like increases when the sample is reverse biased. The nature of these steps, which depends upon the temperature, exciting wavelength and intensity and the number of quantum wells (QWs) in the device, is explained in terms of thermionic emission and negative charge accumulation due to the low confinement of holes in GaInNAs QWs. At high temperature, thermal escape from the wells becomes much more dominant and the steps smear out.
Keywordsp-i-n diodes GaInNAs/GaAs Multiple quantum well Dilute nitrides
Dilute nitride research has sparked considerable interest from fundamental physics to industrial applications, and nowadays, several devices based on GaInNAs/GaAs heterostructures are commercially available [1–7]. The interest on this material started from the discovery that adding small amounts of nitrogen to GaAs and GaInAs resulted in a relatively large redshift in bandgap , leading to the realisation of 1.3- and 1.55 μm wavelength devices  with strong electron confinement with the use of the well-established GaAs technology.
Extensive work has been carried out on dilute nitrides, and the demonstration of dilute nitride-based LEDs, lasers [10–12] and solar cell devices  has already been achieved. In a recently published study , we observed several oscillations in the current-voltage (I V) characteristics of p-i-n GaInNAs/GaAs multiple quantum well (MQW) structures at low temperature under illumination. By performing the experiment at different photon wavelengths, it was established that the optical transitions in GaInNAs quantum wells were the origin of these oscillations. In this paper, we further investigate the oscillations by studying at the photoluminescence under bias. These results give a more complete understanding of the underlying mechanisms such as thermal escape, trapping, recombination and charge accumulation.
The structure studied was a Ga0.952In0.048N0.016As0.984/GaAs p-i-n photodiode grown by molecular beam epitaxy (MBE) on an n-doped (100) oriented GaAs substrate. The intrinsic region consists of 10 undoped GaInNAs QWs with varying thickness from 3.8 to 11 nm. The wells were separated from each other by 20 nm thick and from the bulk region by 40 nm intrinsic GaAs barriers. The active region is sandwiched between a 250 nm Be p-doped GaAs layer with doping density of 2 × 1018 cm−3 and a 600 nm Si n-GaAs layer with 5 × 1017 cm−3 doping density. The sample [see Additional file 1 was fabricated in the shape of a mesa-structure, with top circular aperture of 1 mm diameter. Further details about growth and fabrication can be found in our previous publication .
Results and discussion
where is the effective mass for the carriers in the well; Ebarrier is the energy difference between the sub-band and the barrier; and L is the well width.
Photocurrent and integrated photoluminescence measurements on a GaInNAs/GaAs multi-quantum well based p-i-n diode are performed at T = 100 K as a function of applied bias. The analysis reveals that under reverse bias, clear oscillations in the PC and PLb signals are observed. The difference in the thermal escape time of electrons and holes causes the accumulation of negative charge in the wells giving rise to the observed current oscillations.
We would like to thank COST action MP0805 and EPSRC grant EP/P503965/01 grants for their funding. We are also grateful to Tampere University of Technology, Optoelectronics Research Centre, Finland for growing the samples.
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