Photocurrent spectroscopy and hydrostatic-pressure-dependent electroluminescence are used to show that heavy $1\times {10}^{19}{\mathrm{cm}}^{-3}$ Si doping of quantum barriers is sufficient to achieve full screening of polarization-induced electric fields (PIEFs) in nitride light emitting diodes (LEDs) and laser diodes (LDs) with InGaN quantum wells. Furthermore, it is shown that at currents close to lasing threshold in nitride LDs injected charge alone is sufficient to achieve full screening of PIEFs. In contrast, full screening at low currents can only be accomplished via Si doping of quantum barriers.

The emission wavelength of broad-area AlGaInP/InGaP quantum-well lasers is tuned by the application of high hydrostatic pressure and low temperature from 645 down to 575 nm, i.e., from the red through the orange to yellow spectral range. Emission powers up to 300 mW are obtained in the full tuning range. The pressure and temperature dependence of threshold currents indicates that leakage occurs into the $L$ and $X$ minima in the barriers.

We demonstrate efficient wavelength tuning by means of hydrostatic pressure of an InGaN/GaN laser diode grown on bulk GaN crystal. Energy shifts of the emitted light with pressure have been found to be about 36 meV/GPa, which are high magnitudes for nitride-based device structures. This result is interpreted as being indicative of efficient screening of built-in electric fields in the studied device. Furthermore, the threshold current of the laser diode was found to be independent of applied pressure. The high magnitude of the pressure coefficient allowed for the achievement of a laser tuning range of up to 10 nm in the blue/violet region, using compact pressure equipment.

$\mathrm{In}\mathrm{Ga}\mathrm{As}\mathrm{Sb}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}\mathrm{Sb}$ type-I midinfrared diode lasers emitting continuous wave at $2.4\mu \mathrm{m}$ at room temperature have been studied under high hydrostatic pressure. When the pressure was increased up to $19\mathrm{kbar}$ , the threshold current varied from $240\text{to}400\mathrm{A}∕{\mathrm{cm}}^2$ , showing a minimum of $200\mathrm{A}∕{\mathrm{cm}}^2$ close to $8\mathrm{kbar}$ , and the emission spectra shifted to shorter wavelengths by up to $700\mathrm{nm}$ (i.e., from $2.4\mu \mathrm{m}\text{to}1.7\mu \mathrm{m}$ ). This exceptional tuning range could be very useful in tunable diode laser absorption spectroscopy.

In this paper we review the recent studies on wide InGaN quantum wells (QWs). InGaN QWs are known to suffer from an extremely high built-in piezoelectric polarization, which separates the electron and hole wavefunctions and causes the quantum-confined Stark effect. We show both by means of modeling and experimentally, that wide InGaN QWs can have quantum efficiency superior to commonly used thin QWs. The high efficiency is explained by initial screening of the piezoelectric field and subsequent emergence of optical transitions involving the excited states of electrons and holes, which have a high oscillator strength. A high pressure spectroscopy and photocurrent measurements are used to verify the mechanism of recombination through excited states. Furthermore, the influence of QW width on the properties of optoelectronic devices is studied. In particular, it is shown how the optical gain forms in laser diodes with wide InGaN QWs.