D. C. Grillo

Blue‐green injection laser diodes in (Zn,Cd)Se/ZnSe quantum wells

Laser diode action in the blue‐green has been observed from (Zn,Cd)Se quantum wells within ZnSe/Zn(S,Se) p‐n heterojunctions up to 250 K. Operation is reported for two different configurations for which the GaAs substrate serves either as the n‐ or p‐type injecting contact. In pulsed operation, output powers exceeding 0.6 W have been measured in devices prepared on both n‐type and p‐type GaAs epitaxial buffer layers and substrates.

Blue and green diode lasers in ZnSe‐based quantum wells

Laser diode operation has been obtained from (Zn,Cd)Se/ZnSe and (Zn,Cd)Se/Zn(S,Se) quantum well structures in the blue and the green. The devices, prepared on p‐ and n‐type (In,Ga)As or GaAs buffer layers for lattice matching purposes to control the defect density, have been operated at near‐room‐temperature conditions and briefly at room temperature with uncoated end facets. Quasi‐continuous wave operation has been obtained at T=77 K.

Microstructure study of a degraded pseudomorphic separate confinement heterostructure blue‐green laser diode

The microstructure of a degraded II‐VI blue‐green laser diode based on the ZnCdSe/ZnSSe/ ZnMgSSe pseudomorphic separate confinement heterostructure has been examined by transmission electron microscopy. Triangular nonluminescent dark defects observed in the laser stripe region by electroluminescence microscopy have been identified to be dislocation networks developed at the quantum‐well region. The dislocation networks have been observed to be nucleated at threading dislocations originating from pairs of V‐shaped stacking faults which are nucleated at or near the II‐VI/GaAs interface and extending into the n‐ZnMgSSe lower cladding layer.

Room temperature blue light emitting p-n diodes from Zn(S,Se)-based multiple quantum well structures

Blue (494 nm) light emitting quantum well diodes based on Zn(S,Se) p‐n junctions are demonstrated at room temperature. P‐type Zn(S,Se) is realized by using a nitrogen rf plasma cell. The light emitting diode is formed on homoepitaxial GaAs buffer layers by molecular beam epitaxy. The S fraction of the alloy is selected to provide a lattice match between the II‐VI active region and the GaAs buffer; the result is an active region having a dislocation density below 105/cm−2. The letter discusses emission characteristics as well as the x‐ray rocking curve and transmission electron microscopy characterization of the structures.

Blue/green pn junction electroluminescence from ZnSe‐based multiple quantum‐well structures

The successful p doping of ZnSe by substitutional nitrogen using a plasma cell incorporated into the molecular beam epitaxy chamber has led to the development of electroluminescent devices based on carrier injection at a pn junction. The light emitting diode structures described here are grown on a GaAs substrate using a tetragonally distorted (In,Ga)As buffer layer to provide lattice matching between the substrate and the active II–VI region. The result of the incorporation of the buffer layer is an essentially dislocation‐free active region. The letter discusses optical properties as well as the x‐ray and transmission electron microscopy characterization of the quantum well device structures.

Indium tin oxide as transparent electrode material for ZnSe‐based blue quantum well light emitters

Sputter deposited indium tin oxide layers have been used as the top contact for blue LEDs and diode lasers in (Zn,Cd)Se/Zn(S,Se) quantum well heterostructures. The contact resistance to n‐Zn(S,Se) is comparable to that with indium or gold. The optically transparent contacts have been utilized, as an example, in the fabrication of a numeric display device and to show that LED emission is of excitonic origin in these type I quantum wells.

Blue‐green laser emission from ZnSe quantum well microresonators

Microresonator structures have been fabricated from (Zn,Cd)Se/Zn(S,Se) quantum well material. The resonators, which are designed in the ‘‘whispering gallery’’ geometry, have been optically pumped at room temperature with threshold excitation levels of 100 kW/cm2.

On degradation of ZnSe‐based blue‐green diode lasers

The degradation mechanism of ZnMgSSe/ZnSSe/ZnCdSe separate confinement heterostructure laser diodes is studied under continuous wave and pulsed operation at room temperature. The degradation of the active quantum well is caused by formation of optically inactive areas which nucleate at paired stacking faults. These ‘‘dark defects’’ are identified as areas of dislocation network and point defect segregation.

Pseudomorphic separate confinement heterostructure blue-green diode lasers

The growth and performance of pseudomorphic separate confinement heterostructure blue‐green laser diodes are described. The devices incorporate the (Zn,Mg)(S,Se) quaternary as cladding layers surrounding a Zn(S,Se) waveguiding layer, and having single or multiple quantum wells of (Zn,Cd)Se. Devices have been operated at room temperature under pulsed conditions (∼1 μs, 10−3 duty cycle) for periods up to 1 h. X‐ray rocking curve full width at half‐maxima as low as 44 arcsec were obtained for a laser structure employing quaternary cladding layers (Mg=9%, S=12%), consistent with transmission electron microscope observations showing no dislocations or stacking faults. The Zn(Se,Te) graded contact was adapted to form an ohmic contact to the top p‐type quaternary layer.

Ohmic contacts and transport properties in ZnSe-based heterostructures

In this paper both horizontal and vertical transport properties of ZnSe based heterostructures were studied. Temperature-dependent Hall effect measurements were performed on nitrogen-doped ZnSe, ZnTe, Zn(S,Se) and (Zn,Mg)(S,Se) epilayers; accepter concentration N a , compensation donor concentration N d and the activation energy E a were derived by curve-fitting to the freeze-out behavior of the hole concentrations. Vertical transport study, through the use of an analytical computer simulation, suggested that the electron transport across the n-ZnSe/n-GaAs heterointerfacc is often hindered by the presence of a high density of interface states; both the employment of heavy doping near the interface and the modification of GaAs surface stoichiometry before the nucleation of ZnSe were found effective in reducing the device impedance