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Compositional dependence of the ordering probability in GayIn(1−y)P epitaxial layers grown on GaAs substrates is investigated. Experimental results reveal that band‐gap energy reduction due to the ordering is varied with the Ga composition of GayIn(1−y)P and shows a dependence on growth temperature in a wide range of Ga compositions where no serious lattice mismatch occurs. In addition, the change of the ordering of GayIn(1−y)P is confirmed by transmission electron diffraction patterns. For the calculation of the relative ordering probability of the GayIn(1−y)P alloy, a model representing an ordering state with alternative stacking of two tetrahedral micro‐unit cells (three Ga‐P‐one In)/(one Ga‐P‐three In), is proposed. The results of the calculation on the compositional dependence of ordering probability, which are based on internal strain energy states of the unit cells of the GayIn(1−y)P alloy, show good agreement with experimental results.

A new graded InxGa(1−x)As/GaAs/AlGaAs strained‐layer single quantum well (QW) laser diode has been proposed and experimentally characterized. Bias‐dependencies of valence subbands and maximum optical gains of the InGaAs QW on the external bias are calculated taking into account the effects of the valence band mixing and intraband relaxation. Electron distributions in the conduction bands at threshold bias are also calculated by solving the Poisson and Schrodinger equation self‐consistently. By a two‐step grading of the InGaAs QW compositions, the higher peak value and smaller full width at half maximum of electron distributions can be obtained around the QW center even at the large external bias. Moreover, the electron‐hole spatial separation is substantially reduced in the graded QW. A graded InxGa(1−x)As/GaAs strained‐layer single QW laser diode with x=0.17–0.33 shows lower threshold current densities by 15% than those of the conventional In0.25Ga0.75As laser.

A new double modulation‐doped AlGaAs/InGaAs heterostructure with a graded composition in the InGaAs quantum well (QW) has been designed and electrically characterized. An InGaAs QW with a rectangular‐like potential profile in the presence of the two dimensional electron gas is obtained by a two‐step grading of the In composition, which results in a broad and symmetric electron distribution profile even under various voltages. The Hall measurement shows a very high electron mobility of 7230 cm2/V s and an electron sheet density of 4.1×1012/cm2 at room temperature. To our knowledge, this is the highest mobility ever reported so far for the double modulation‐doped Al0.3Ga0.7As/In0.2Ga0.8As field‐effect transistor structure.

Polarization‐dependent optical gain of recently demonstrated CdZnSe/ZnSe quantum well lasers is calculated for the first time. Our analysis is based on the multiband effective mass theory (k⋅p theory) and the density matrix formalism with intraband relaxation taken into account. It is shown theoretically that the TE mode gain is significantly larger than the TM mode gain for a wide range of carrier density. Comparison of the room‐temperature TE mode gain of CdZnSe/ZnSe quantum well with that of GaAs/AlGaAs quantum well gives disappointing results for the II‐VI semiconductor lasers. It is expected that the optical gain of the ZnSe‐based semiconductor lasers would be substantially smaller than the optical gain of the GaAs‐based semiconductor lasers for a same quantum well width and carrier density.

The effect of silicon doping in the selected barrier on the electroluminescence of InGaN∕GaN multiquantum well light emitting diode (LED) was studied using dual wavelength LEDs. The result verified that the hole carrier transport is easily blocked by the silicon doped barrier, and the dominant electron and hole recombination occurs at the wells between p-GaN and the silicon doped barrier. The electroluminescence spectrum and the wavelength blueshift of the silicon doped LEDs were compared with undoped LEDs. The numerical simulation was done to clearly explain the hole blocking effect by the silicon doped barrier.

To increase the light extraction efficiency, high density truncated hexagonal pyramid shaped submicron p-GaN hillocks were formed on the emission surface of an InGaN∕GaN multiple quantum well light emitting dicode (LED) using an in situ silicon carbon nitride self-masking layer. The self-assembled hillock density was raised up to a low 109cm−2 using several nanometers of a Si0.4C0.6N1 self-masking layer. The self-assembled hillock LED resulted in the optical power improvement up to 80% with similar electrical properties as a normal LED. This device showed a higher electrostatic discharge pass yield at over 1000V reverse stress voltage.

The optical gain and the intraband relaxation time of wurtzite InGaN∕GaN QW lasers are investigated theoretically considering the non-Markovian gain model with many-body effects. Gain spectra are compared with those obtained from the experiment. The calculated intraband relaxation time is about 24fs at the subband edge and gradually increases with the energy. The intraband relaxation time is shown to be nearly independent of the sheet carrier density in an investigated range. The calculated gain spectra is in good agreement with the experiment. The intraband relaxation time τin obtained from fitting with experiment is 25fs. This value agrees well with the calculated value (∼24fs) at the subband edge, for which most of optical transitions occur.