Bulent Aslan

Effect of the Passivation Layer on the Noise Characteristics of Mid-Wave-Infrared InAs/GaSb Superlattice Photodiodes

The authors describe the noise characterization of a mid-wavelength-infrared (MWIR) photodiode based on indium arsenide and gallium antimonide (InAs/GaSb) superlattice (SL), addressing the influence of different passivation layers applied to the surface of the device. The MWIR InAs/GaSb SL design structure is based on p-i-n configuration grown by the molecular beam epitaxy on a (001) n-GaSb substrate. The SiO2-passivated SL photodiodes demonstrated a Schottky-limited noise up to a bias voltage of -0.1 V where the measured peak responsivity is 1.37 AAV with a cut-off wavelength of 4.9 μm and the specific detectivity as high as 1.23 × 1012 cm. Hz1/2 /W, demonstrating the high quality of the fabricated MWIR SL photodiodes. The noise measurements exhibited a frequency-dependent plateau (i.e., 1/f noise) for unpassivated and Si3N4-passivated samples, whereas 1/f-type noise suppression (i.e., frequency-independent plateau) with a noise current reduction at about 30 Hz of more than one order of magnitude was observed for the SiO2-passivated ones.

Binding energies and oscillator strengths of impurity states in wurtzite InGaN/GaN staggered quantum wells

Using the variational methods, we have calculated the binding energies of the lowest donor states, 1s and 2p±, in wurtzite InGaN/GaN staggered quantum wells. The binding energies in narrow wells are larger in magnitude than the values in bulk GaN due to the quantum confinement effects. However, the energies decrease sharply in wider wells because of the weakening confinement due to the strong built-in electric field inside the well. The binding energies of donors placed at the opposite edges of the well are quite different as the built-in electric field forms an asymmetric, triangular potential inside the well. The oscillator strength of the possible transitions between the donor states is then computed by modelling them as the states of a two-level atom. A magnetic field applied along the growth direction splits up the degenerate 2p± states. The amount of splitting in the quantum well is found to be small possibly due to the heavy electron effective mass inside the well. The oscillator strength of the tr...

Donor-related third-order optical nonlinearites in GaAs/AlGaAs quantum wells at the THz region

GaAs/AlGaAs quantum wells doped with donor atoms are investigated for nonlinear optical applications in the THz range. The electronic properties of the quantum wells are obtained numerically by applying an iterative shooting algorithm. Donor binding energies are computed through the evaluation of variational wavefunctions. The solution of the density matrix equations of motion for non-interacting two-level atoms within the rotating wave approximation is used to formulate the third-order optical nonlinearities. Transitions between the 1s and 2p± impurity states because of an incident light polarized perpendicularly to the growth direction are considered as the origins of optical nonlinearity. Following a set of computations for a quantum well doped at the center, it is found that the nonlinear susceptibility decreases when the well becomes wider or the Al concentration increases. Additionally, when the doping center is shifted to the well edge, the nonlinear susceptibility decreases too. A large nonlinear figure of merit is obtainable in wider wells compared to the narrower wells although the latter delivers larger nonlinear susceptibilities.

Comparative evaluation of InAs/GaSb superlattices for mid infrared detection: p-i-n versus residual doping

We report on the opto-electronic characterization of an InAs/GaSb superlattice (SL) midwave infrared p–i–n photodetector structure (pin-SL) in comparison with the same structure with no intentional doping (i-SL). Both structures were grown on an n-GaSb substrate using molecular beam epitaxy. The nominally undoped structure (i-SL) presented p–i–n like behavior and showed a photovoltaic mode photoresponse due to the residual doping and native defects in this material system. For ~77 K operation, 0.76 and 0.11 A W–1 responsivity values were obtained at 4 μm from the pin-SL and i-SL structures, respectively. Activation energy analysis showed that the recombination current was dominant in both structures but different recombination centers were involved. The same i-SL structure was also grown on a semi-insulating (SI)-GaAs substrate to study the contribution of the substrate to the carrier density in the SL layers. Temperature dependent Hall effect measurements showed that the nominally undoped structure presented both n-type and p-type conductivities; however, the temperature at which the carrier type switched polarity was observed to be at higher values when the i-SL structure was grown on the SI-GaAs substrate. In addition, a higher carrier density was observed for i-SL on the GaSb substrate than on the GaAs substrate.

On the donor states in double InxGa1 − xN/InyGa1 − yN/GaN staggered quantum wells

We have calculated the binding energies of the donor states, 1s and 2p?, with respect to the lowest sub-band energy in a double quantum well composed of wurtzite InGaN staggered quantum wells with GaN barriers. All the energies and the wavefunctions were calculated by applying the variational methods. We have found that the binding energies of donors placed in the right quantum well are larger and independent of the middle barrier width of up to 40 ?. This is because of the strong built-in electric field which brings more confinement to the donor wavefunctions in the right staggered quantum well. The binding energies are found to be strong functions of the donor position in the double quantum well system which is the consequence of the large asymmetry introduced by the built-in electric field.

Intersubband transitions in InxGa1−xN/InyGa1−yN/GaN staggered quantum wells

Intersubband transition energies and absorption lineshape in staggered InGaN/GaN quantum wells surrounded by GaN barriers are computed as functions of structural parameters such as well width, In concentrations, and the doping level in the well. Schrodinger and Poisson equations are solved self-consistently by taking the free and bound surface charge concentrations into account. Many-body effects, namely, depolarization and excitonic shifts are also included in the calculations. Results for transition energies, oscillator strength, and the absorption lineshape up to nonlinear regime are represented as functions of the parameters mentioned. The well width (total and constituent layers separately) and In concentration dependence of the built-in electric field are exploited to tune the intersubband transition energies.