Room-temperature optically pumped GaN-based vertical-cavity surface-emitting lasers (VCSELs) were demonstrated by laser lift-off. A VCSEL was fabricated by combining a GaN-based cavity with two dielectric distributed Bragg reflectors: SiO2/TiO2 and SiO2/Ta2O5. The Q factor of the VCSEL is 518 indicating a good interfacial layer quality of the structure. The laser emits blue-violet wavelength light at 414 nm under optical pumping at room temperature with a threshold pumping energy of 270 nJ. The laser emission has a narrow linewidth of 0.25 nm and a degree of polarization of 70%. The laser emission patterns clearly indicate a vertical lasing action of the VCSEL.

Self-assembled InGaN quantum dots (QDs) were grown by metal-organic chemical vapour deposition with growth interruption at low V/III ratio and low growth temperature on sapphire substrates. The effects of the interruption time on the morphological and optical properties of InGaN QDs were studied. The results show that the growth interruption can modify the dimension and distribution of InGaN QDs, and cause the QD emission wavelength to blue shift with increasing interruption time. A density of InGaN QDs of about 4.5 × 10(10) cm(-2) with an average lateral size of 11.5 nm and an average height of 1.6 nm can be obtained by using a growth interruption time of 60 s.

Nonequilibrium electron transport in a high-quality, single-crystal, wurtzite structure InN thin film grown on GaN has been investigated by picosecond Raman spectroscopy. Our experimental results show that an electron drift velocity as high as (5.0±0.5)×107 cm/s can be achieved at T=300 K. The experimental results have been compared with ensemble Monte Carlo simulations and good agreement is obtained. From the comparison, we have also deduced that the built-in electric-field intensity inside our InN thin-film system is about 75 kV/cm.

Large-area p-side-down InGaN light-emitting diodes (LEDs) 1000×1000 µm2 in size have been fabricated by laser lift-off (LLO). The p-side-down LEDs with different geometric patterns of n-electrodes were fabricated to investigate electrode pattern-dependent optical characteristics. The current crowding effect was observed in the large-area p-side-down InGaN LLO-LEDs. A LED with a well-designed n-electrode pattern shows a uniform distribution of light emission and a higher output power due to uniform current spreading. The output power saturation induced by the current crowding effect was investigated. In the absence of a transparent contact layer for current spreading, the n-electrode pattern has a marked influence on the current distribution and the consequent light output power of the large-area p-side-down LEDs.

A large-area GaN-based light-emitting diode (LED) 1000×1000 µm2 in size with a p-side down configuration was fabricated using wafer bonding and laser lift-off (LLO) techniques. The thin GaN LED was transferred onto a copper substrate without peeling or cracks. The large-area LEDs showed a uniform light-emission pattern over entire defined mesa area without a transparent contact layer on the p-type GaN. The operating current of the large-area LEDs can be driven up to 1000 mA with continuously increasing light output-power. The light output-power is 240 mW with a driving current of 1000 mA. Large-area emission and high current operation make the LLO-LEDs applicable to high-power LED applications.

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We have experimentally proven the Cerenkov generation of optical phonons by drifting electrons in a semiconductor. We observe an instability of the polar optical phonons in nanoscale semiconductors that occurs when electrons are accelerated to very high velocities by intense electric fields. The instability is observed when the electron drift velocity is larger than the phase velocity of optical phonons and rather resembles a ''sonic boom'' for optical phonons. The effect is demonstrated in p-in semiconductor nanostructures by using subpicosecond Raman spectroscopy.

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