Hagir Mohammed Khalil

Carrier trapping and escape times in p-i-n GaInNAs MQW structures

We used a semi-classical model to describe carrier capture into and thermionic escape from GaInNAs/GaAs multiple quantum wells (MQWs) situated within the intrinsic region of a GaAs p-i-n junction. The results are used to explain photocurrent oscillations with applied bias observed in these structures, in terms of charge accumulation and resonance tunnelling.

Photoconductivity and photoluminescence under bias in GaInNAs/GaAs MQW p-i-n structures

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.

Experimental investigation and numerical modelling of photocurrent oscillations in lattice matched Ga1−xInxNyAs1−y/GaAs quantum well p-i-n photodiodes

Photocurrent oscillations, observed at low temperatures in lattice-matched Ga1−xInxNyAs1−y/GaAs multiple quantum well (MQW) p-i-n samples, are investigated as a function of applied bias and excitation wavelength and are modelled with the aid of semiconductor simulation software. The oscillations appear only at low temperatures and have the highest amplitude when the optical excitation energy is in resonance with the GaInNAs bandgap. They are explained in terms of electron accumulation and the formation of high-field domains in the GaInNAs QWs as a result of the disparity between the photoexcited electron and hole escape rates from the QWs. The application of the external bias results in the motion of the high-field domain towards the anode where the excess charge dissipates from the well adjacent to anode via tunnelling.

Photocurrent oscillations in GaInNAs / GaAs multi-quantum well p-i-n structures

In this work the photoconductivity of a p-i-n Ga0.952In0.048N0.016As0.984/GaAs multiple quantum well (MQW) structure is investigated as a function of temperature. At low temperatures step-like increases are observed in the devices I–V characteristic when illuminated with a 950nm wavelength light. The number of visible oscillations varies according to the temperature and incident light intensity with a maximum of 18 being visible. Since the exciting illumination energy is bellow the GaAs bandgap, these oscillations arise only from the GaInNAs quantum wells and can be explained in terms of resonant tunneling from subbands into the adjacent quantum well.

Investigation of MQW GaInNAs/GaAs p-i-n photodetector

Transient photoconductivity (TPC), detectivity (D), and noise-equivalent power (NEP) in a dilute nitride based GaInNAs/GaAs multiple quantum well photodetector operating at λ >;1.3 μm are investigated at different temperatures from 100 to 300K. In this temperature range the TPC rise time increases from around 2 ns to 4 ns. The decay PC decays exponentially with two time constants; the fast one of about 5 ns which is independent on temperature, is followed by a slower one of 200 ns at T=100 K, and 520 ns at room temperature. The maximum detectivity of the photodetector is 6.6×109cm√(Hz)/W and the minimum NEP is 3.6×10-11W/√(Hz), indicating a reasonably fast and sensitive low-noise photodetector.

Nonlinear dynamics of non-equilibrium holes in p-type modulation-doped GaInNAs/GaAs quantum wells

Nonlinear charge transport parallel to the layers of p-modulation-doped GaInNAs/GaAs quantum wells (QWs) is studied both theoretically and experimentally. Experimental results show that at low temperature, T = 13 K, the presence of an applied electric field of about 6 kV/cm leads to the heating of the high mobility holes in the GaInNAs QWs, and their real-space transfer (RST) into the low-mobility GaAs barriers. This results in a negative differential mobility and self-generated oscillatory instabilities in the RST regime. We developed an analytical model based upon the coupled nonlinear dynamics of the real-space hole transfer and of the interface potential barrier controlled by space-charge in the doped GaAs layer. Our simulation results predict dc bias-dependent self-generated current oscillations with frequencies in the high microwave range.

Magnetic field effect on current oscillations observed in p-i-n GaInNAs/GaAs multiple quantum wells structures

The photoconductivity (PC) of two p-i-n GaInNAs/GaAs multiple quantum well (MQW) mesa structures is investigated. When illuminated with photons at energy greater than the GaAs bandgap, at low temperature a number of oscillations are observed in the current-voltage (I-V) characteristics. We found that the position of these oscillations depend upon on the temperature and the magnetic field. Due to the absence of the oscillations in the dark and in the PC at temperatures above 200 K, we explain them in terms of photogenerated electrons thermally escaping from the quantum wells and carrier accumulation. Magnetic fields up to 11 T were applied parallel to the planes of the QWs. A small voltage shift in the position of the oscillations was observed, proportional to the magnetic field intensity and dependent upon the temperature. Calculation of the Landau level energy separation (16 meV) agrees with the observed experimental data.

Current oscillations in multiple quantum well GaInNAs/GaAs p-i-n structures

Summary form only given. Photoconductivity in reverse and forward biased Ga 0.952 In 0.048 N 0.016 As 0.984 /GaAs multiple quantum well p-i-n structures is investigated in a temperature range between T = 20 K and 300 K. When the samples are under illumination with photons, ħω > EG (GaAs), the I–V characteristics show current oscillations whose amplitude depends on the temperature, wavelength and intensity of the excitation, and the number of QWs in the device. (Up to 8 and 18 oscillations have been observed in the 10 and 20 MQW devices respectively). They disappear at temperatures above T ∼ 200 K and the oscillations are not present in darkness. We propose a model to account for the observations based on the carrier tunneling and thermionic emission in the GaInNAs QWs. Comparative studies on p-i-n and n-i-p type structures are also performed.