We report the observation of optically pumped lasing in ZnO at room temperature. Thin films of ZnO were grown by plasma-enhanced molecular beam epitaxy on (0001) sapphire substrates. Laser cavities formed by cleaving were found to lase at a threshold excitation intensity of 240 kW cm−2. We believe these results demonstrate the high quality of ZnO epilayers grown by molecular beam epitaxy while clearly demonstrating the viability of ZnO based light emitting devices.

Optically pumped lasing of ZnO at room temperature

http://nathan.instras.com/documentDB/paper-44.pdf

Surface photovoltage phenomena: theory, experiment, and applications

A II-VI compound semiconductor laser diode (10) is formed from overlaying layers of material including an n-type single crystal semiconductor substrate (12), adjacent n-type and p-type guiding lasers (14) and (16) of II-VI semiconductor forming a pn junction, a quantum well active layer (18) of II-VI semiconductor between the guiding layers (14) and (16), first electrode (32) opposite the substrate (12) from the n-type guiding layer (14), and a second electrode (30) opposite the p-type guiding layer (16) from the quantum well layer (18) Electrode layer (30) is characterized by a Fermi energy A p-type ohmic contact layer (26) is doped, with shallow acceptors having a shallow acceptor energy, to a net acceptor concentration of at least 1 x 1017 cm-3, and includes sufficient deep energy states between the shallow acceptor energy and the electrode layer Fermi energy to enable cascade tunneling by charge carriers

Blue-green laser diode

During the last few years the developments in the field of III–nitrides have been spectacular. High quality epitaxial layers can now be grown by MOVPE. Recently good quality epilayers have also been grown by MBE. Considerable work has been done on dislocations, strain, and critical thickness of GaN grown on different substrates. Splitting of valence band by crystal field and by spin-orbit interaction has been calculated and measured. The measured values agree with the calculated values. Effects of strain on the splitting of the valence band and on the optical properties have been studied in detail. Values of band offsets at the heterointerface between several pairs of different nitrides have been determined. Extensive work has been done on the optical and electrical properties. Near band-edge spectra have been measured over a wide range of temperatures. Free and bound exciton peaks have been resolved. Valence band structure has been determined using the PL spectra and compared with the theoretically calcu...

III–nitrides: Growth, characterization, and properties

A novel approach to producing p‐type ZnSe epitaxial layers is reported which involves nitrogen atom beam doping during molecular beam epitaxial growth. Net acceptor concentrations as large as 3.4×1017 cm−3 have been measured in nitrogen atom beam doped ZnSe/GaAs heteroepitaxial layers which represents the highest acceptor concentration reported to date for ZnSe:N epitaxial material grown by molecular beam epitaxy. In addition, light‐emitting diodes based on ZnSe:N/ZnSe:Cl, p‐n homojunctions have been found to exhibit dominant electroluminescence in the blue region of the visible spectrum at room temperature.

p-type ZnSe by nitrogen atom beam doping during molecular beam epitaxial growth

Optical characterization and band offsets in ZnSe-ZnSxSe

An image display system utilizes primarily non-absorptive polarization components to polarize light illuminating an imaging device. The non-absorptive polarization components reduce cost and cooling requirements, increase durability, and permit the use of high powered light sources.

Image display system

We present low‐temperature photoluminescence and transmission electron microscopy data to show that two transitions I0V at ∼2.774 eV and Y0 at ∼2.60 eV, frequently observed in unintentionally doped zinc selenide epitaxial layers, are directly related to structural defects. It is shown that these transitions are strong in those samples which have very low background impurities and high density of structural defects and weak in those cases that have either high background impurities or low density of structural defects.

Correlation between radiative transitions and structural defects in zinc selenide epitaxial layers

The elastic strains in regions near the top surface of strained-layer structures can be quite different from those in deeper portions of the samples. This effect has been established in epitaxial layers of ZnSe grown on GaAs and ZnSe-$\mathrm{Zn}{\mathrm{S}}_{x}{\mathrm{Se}}_{1\ensuremath{-}x}$ strained-layer superlattices. The depth dependence of the strains was determined with Raman scattering measurements performed under laser excitation below and above the band gap. The strain values near the top surface are driven by a stronger relaxation of the in-plane lattice constants towards equilibrium. This relaxation appears to be independent of the generation of misfit dislocations.

Depth profiling of elastic strains in lattice-mismatched semiconductor heterostructures and strained-layer superlattices.

We report a novel technique to obtain p‐type ZnSe layers doped with nitrogen. The layers were grown in a low‐pressure metalorganic vapor phase epitaxy system using ammonia as the dopant source. A rapid thermal anneal was used to enhance the activation of the nitrogen acceptors. Net acceptor concentration values as high as 3×1016/cm3 were obtained from capacitance‐voltage measurements and the profile was uniform over the thickness of the epitaxial layers. The 7 K photoluminescence spectrum was dominated by the acceptor bound exciton peak; the donor‐acceptor pair spectra were also observed.

Khalid Shahzad

Papers

Optical characterization and band offsets in ZnSe-ZnSxSe

Image display system

Correlation between radiative transitions and structural defects in zinc selenide epitaxial layers

Depth profiling of elastic strains in lattice-mismatched semiconductor heterostructures and strained-layer superlattices.

Novel technique for p‐type nitrogen doped ZnSe epitaxial layers