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

Esmaeili M., Gholami M., Haratizadeh H., Monemar B., Holtz P. O., Kamiyama S., Amano H., Akasaki I.

Opto-Electronics Review

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2009

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Vol. 17, No. 4

293-299

EN

We report the results from detailed optical spectroscopy from MOCVD grown GaN/AlGaN multiple quantum wells (MQWs), as opposed to most previous studies where MBE was employed by means of photoluminescence (PL) technique. In this paper we will present theoretical and experimental results demonstrating how polarization induced electric fields and bound interface charges in GaN/AlGaN MQWs affect the emission peak energy, PL line shape, as well as the emission line width. Theoretically estimated fields in this work are consistent with experimental data. Transition energy of the heavy hole and electron ground state Ee-hh in GaN/AlGaN MQWs were calculated and it is found that it stays in good agreement with the experimental data.

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Exciton localization behaviour in different well width undoped GaN/Al₀.₀₇Ga₀.₉₃N nanostructures

Sabooni M., Esmaeili M., Haratizadeh H., Monemar B., Paskov P., Kamiyama S., Iwaya M., Amano H., Akasaki I.

Opto-Electronics Review

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2007

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Vol. 15, No. 3

163-167

EN

We report results from optical spectroscopy such as photoluminescence (PL) and time resolved photo-luminescence (TRPL) techniques from different well width MOCVD grown GaN/Al₀.₀₇Ga₀.₉₃N MQW samples. There is evidence of localization at low temperature in all samples. The decay time of all samples becomes non-exponential when the detection energy is increased with respect to the peak of the emission. Localization of carriers (excitons) is demonstrated by the "S-shape" dependences of the PL peak energies on the temperature. The time-resolved PL spectra of the 3-nm well multi quantum wells reveal that the spectral peak position shifts toward lower energies as the decay time increases and becomes red-shifted at longer decay times. There is a gradient in the PL decay time across the emission peak profile, so that the PL process at low temperatures is a free electron-localized hole transition.

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Heteroepitaxial technology for high-efficiency UV light-emitting diode

Kamiyama S., Iwaya M., Amano H., Akasaki I.

Opto-Electronics Review

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2002

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Vol. 10, No. 4

225-230

EN

A high-quality AlGaN layer with a low density of threading dislocations is realised for the use of ultraviolet (UV) light-emitting diodes (LEDs). The new crystal growth method of using a GaN seed crystal with (1122) facets and lateral growth of Al₀.₂₂Ga₀.₇₈N through the low -temperature-deposited AlN interlayer enalbles the overgrown Al₀.₂₂Ga₀.₇₈N to have a low dislocation density of 2 x 10⁷ cm⁻² and be crack-free over the whole wafer. Applying the AlGaN as a base layer in UV-LEDs, high - performance devices with high output powers of more than 0.1 mW under 50 mA drive are demonstrated in a wide range of emission wavelengths from 323 to 363 nm. The highest output power of 1.2 mW at 50 mA driving current is obtained with 363 - nm emission wavelength.