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Influence of Built-in Electric Field on Forbidden Transitions in In_xGa_{1-x}As/GaAs Double Quantum Well by Three-Beam Photoreflectance

100%

Sęk G., Ryczko K., Misiewicz J., Bayer M., Wang T., Forchel A.

Acta Physica Polonica A

2001

vol. 100

issue 3

417-424

Photoreflectance spectroscopy has been used to study optical transitions in In_{0.045}Ga_{0.955}As/GaAs double quantum well at 80 K. The derivative nature of this contactless electromodulation technique allows for the observation of excited state transitions in the low-dimensional structure including the symmetry-forbidden ones. Excitonic symmetry-forbidden transitions can be observed due to the effect of mixing of heavy and light hole excitons and/or due to some asymmetry in the structure. We have shown that the built-in electric field in the region of double quantum well is weak enough (less than 0.5 kV/cm) not to cause any significant energetic shift of features due to quantum confined Stark effect, on one hand. On the other hand, it is sufficient to change strongly the oscillator strength of forbidden transitions. To change the internal electric field, we have used photoreflectance in the three-beam mode with a third beam continuously illuminating the sample and causing changes of the built-in electric fields due to the photovoltage effect. This method works as a contactless forward bias and allows for a change of the field down to the flat band conditions. We have shown that changes of built-in electric field by amount of a few tenths of kV/cm can modify the intensity of forbidden transitions significantly. We show that, although the mixing of excitons is still important, a very weak built-in electric field can be dominant in the observation of forbidden excitonic transitions in double quantum well.

Normal Incidence Mid-Infrared Photocurrent in AlGaN/GaN Quantum Well Infrared Photodetectors

68%

Sherliker B., Halsall M., Harrison P., Jovanović V., Indjin D., Ikonić Z., Parbrook P., Whitehead M., Wang T., Buckle P., Phillips J., Carder D.

Acta Physica Polonica A

2005

vol. 107

issue 1

174-178

We report the growth and characterization of AlGaN/GaN multiple quantum well structures designed to have intersubband transitions in the mid-infrared region of the spectrum. The samples were nominally undoped but were found to contain a high electron population in the wells induced by the local polarization fields. The sample was characterized by the use of the Raman spectroscopy and photocurrent spectroscopy. The Raman spectroscopy shows electronic Raman scattering from intersubband transitions in the AlGaN/GaN quantum wells. The e_1-e_2 and e_1-e_3 transitions of the confined 2d electron population in the wells can clearly be observed. A sample designed to absorb at 4μm was fabricated into mesa structures and the vertical photocurrent measured under normal incidence illumination from the free-electron laser FELIX. A wavelength and bias dependent photocurrent was observed in the mid-IR region of spectrum. The peak responsivity was of the order of 50μA/W at 4 K, the photocurrent still being measurable at room temperature.

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2 Acta Physica Polonica A

1 2005

1 2001

2 Wang T.

1 Bayer M.

1 Buckle P.

1 Carder D.

1 Forchel A.

1 Halsall M.

1 Harrison P.

1 Ikonić Z.

1 Indjin D.

1 Jovanović V.

1 Misiewicz J.

1 Parbrook P.

1 Phillips J.

1 Ryczko K.

1 Sherliker B.

1 Sęk G.

1 Whitehead M.

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Influence of Built-in Electric Field on Forbidden Transitions in In_xGa_{1-x}As/GaAs Double Quantum Well by Three-Beam Photoreflectance

Normal Incidence Mid-Infrared Photocurrent in AlGaN/GaN Quantum Well Infrared Photodetectors