Mike D. Ringle

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.

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

D (donor) X center behavior for holes implied from observation of metastable acceptor states

The observation of persistent photoconductivity in nitrogen‐doped p‐ZnMgSSe at low temperature is reported. The increase of conductivity after illumination appears due to a metastable population of holes which are in thermodynamic equilibrium with hydrogenic acceptors having reduced activation energy. The experimental evidence suggests the presence of a DX‐like [D (donor) X center] behavior for holes.

Molecular beam epitaxial growth and characterization of II-VI blue-green laser diodes having continuous-wave operation at room temperature

Abstract Continuous-wave laser operation at room temperature was obtained from a (Zn,Mg)(S,Se)-based II–VI separate-confinement heterostructure where injection of holes into the p-type quaternary was achieved through the employment of a Zn(Se,T) graded-bandgap contact. The laser devices exhibit threshold current densities of below 300 A cm −2 and voltages below 6 V. Issues related to the control of the growth of the quaternary (Zn,Mg)(S,Se) compound are discussed and comments are made on the origins of device degradation.

Pseudomorphic SCH blue-green diode lasers

Summary form only given. The use of the quaternary (Zn,Mg)(S,Se) in a diode laser operating at 77 K has been reported. Such a quaternary compound can maintain lattice compatibility to GaAs with increased bandgap for the implementation of separate confinement heterostructure (SCH) quantum-well lasers. In the present work, the authors describe efforts to employ the quaternary in pseudomorphic SCH diode configurations. These preliminary devices (without heat sinking or coated facets) have been operated at room temperature under pulsed conditions ( approximately 1 mu s, 10/sup -3/ duty cycle) for periods exceeding 1/2 h before failure. A group at Phillips laboratories has recently obtained nearly 400 K operation with 10 to 50 ns pulses in a similar structure. >

Microstructure study of failure mechanism of II-VI blue-green laser diodes

The rapid degradation mechanism of current II-VI blue-green laser diodes based on the pseudomorphic ZnCdSe/ZnSSe/ZnMgSSe separate confinement heterostructures (SCHs) grown by MBE has been studied by using electroluminescence (EL) and transmission electron microscopy (TEM). Nonluminescent dark defects observed in the laser diodes have been identified to be dislocation networks consisting of branches of dislocation dipoles developed at the quantum well region. Stacking fault-dislocation complexes introduced into the laser structure during the MBE growth have been found to be the origin for the nucleation of the dislocation networks. The experimental results indicate that the point defect density at the quantum well region can be reduced by optimizing the growth conditions of the region.

Issues of epitaxial growth and transport for room temperature cw blue/green laser diodes

The growth of ZnMgSSe is a key component of long-lived II-VI laser diodes, however there are structural and electrical problems associated the compound that must be resolved. Precise lattice matching requires accurate growth temperature control due to the dependance of the sulfur sticking coefficient on the growth temperature. Electrically, p-type doping of ZnMgSSe is complicated by an apparent increase in the activation energy caused by a mechanism very much like that of the DX center in n-type III-V alloys. These factors must be addressed for II-VI light emitting devices in deep blue part of the spectrum.

Physics of gain and stimulated emission in II-VI diode lasers

Spectroscopic work is reviewed which focuses on the microscopic mechanism of gain in ZnSe-based quantum well (QW) lasers, under optical and electrical injection, respectively. Excitonic processes are rather distinct at cryogenic temperatures in the strongly quasi-2 dimensional case of a ZnCdSe QW. More strikingly, recent studies on the room temperature diode lasers show that electron-hole pairwise Coulomb correlations remain relevant in this case as well.

Epitaxial growth of quaternary (Zn,Mg)(S,Se) for pseudomorphic separate confinement heterostructure (SCH) laser structures

We report the molecular beam epitaxial growth of the quaternary (Zn,Mg)(S,Se) compound as well as the incorporation of this quaternary into a pseudomorphic SCH blue-green laser diode configuration. X ray diffraction and TEM imaging indicate that the quaternary (Zn,Mg)(S,Se) can accommodate substantially more strain than the binary ZnSe; pseudomorphic epilayers with thickness of about 2 micrometers could be grown within a strain range of -0.225% (tension) and 0.137% (compression) at room temperature. Room temperature continuous wave operation of diode lasers having the quaternary as cladding layers was achieved with a lifetime of longer than 20 seconds. These index-guided laser diodes, employing the Zn(Se,Te) graded ohmic contact (adopted to contact p-type (Zn,Mg)(S,Se), have provided a significant reduction in lasing threshold voltage to 4.2 V.