George John Zydzik

Resonant cavity light‐emitting diode

A novel concept of a light‐emitting diode (LED) is proposed and demonstrated in which the active region of the device is placed in a resonant optical cavity. As a consequence, the optical emission from the active region is restricted to the modes of the cavity. Resonant cavity light‐emitting diodes (RCLED) have higher spectral purity and higher emission intensity as compared to conventional light emitting diodes. Results on a top‐emitting RCLED structure with AlAs/AlxGa1−xAs quarter wave mirrors grown by molecular beam epitaxy are presented. The experimental emission linewidth is 17 meV (0.65 kT) at room temperature. The top‐emission intensity is a factor of 1.7 higher as compared to conventional LEDs.

Ga2O3 films for electronic and optoelectronic applications

Properties of Ga2O3 thin films deposited by electron‐beam evaporation from a high‐purity single‐crystal Gd3Ga5O12 source are reported. As‐deposited Ga2O3 films are amorphous, stoichiometric, and homogeneous. Excellent uniformity in thickness and refractive index was obtained over a 2 in. wafer. The films maintain their integrity during annealing up to 800 and 1200 °C on GaAs and Si substrates, respectively. Optical properties including refractive index (n=1.84–1.88 at 980 nm wavelength) and band gap (4.4 eV) are close or identical, respectively, to Ga2O3 bulk properties. Reflectivities as low as 10−5 for Ga2O3/GaAs structures and a small absorption coefficient (≊100 cm−1 at 980 nm) were measured. Dielectric properties include a static dielectric constant between 9.9 and 10.2, which is identical to bulk Ga2O3, and electric breakdown fields up to 3.6 MV/cm. The Ga2O3/GaAs interface demonstrated a significantly higher photoluminescence intensity and thus a lower surface recombination velocity as compared to ...

Highly Efficient Light-Emitting Diodes with Microcavities

One-dimensional microcavities are optical resonators with coplanar reflectors separated by a distance on the order of the optical wavelength. Such structures quantize the energy of photons propagating along the optical axis of the cavity and thereby strongly modify the spontaneous emission properties of a photon-emitting medium inside a microcavity. This report concerns semiconductor light-emitting diodes with the photon-emitting active region of the light-emitting diodes placed inside a microcavity. These devices are shown to have strongly modified emission properties including experimental emission efficiencies that are higher by more than a factor of 5 and theoretical emission efficiencies that are higher by more than a factor of 10 than the emission efficiencies in conventional light-emitting diodes.

High-power laser light source for near-field optics and its application to high-density optical data storage

A laser light source for high-resolution near-field optics applications with an output power exceeding 1 mW (104 times the power from previous sources) and small (300 nm square to less than 50 nm square) output beam size is demonstrated. The very-small-aperture laser (VSAL) tremendously expands the range of applications possible with near-field optics and increases the signal-to-noise ratios and data rates obtained in existing applications. As an example, 250-nm-diam marks corresponding to 7.5 Gb/in.2 storage density have been recorded and read back in reflection and transmission on a rewritable phase-change disk at 24 Mb/s with a 250-nm-square aperture VSAL. VSALs potentially enable data storage densities of over 500 Gb/in.2 (up to 100 times today’s magnetic or optical storage densities).

Dielectric properties of electron‐beam deposited Ga2O3 films

We have fabricated high quality, dielectric Ga2O3 thin films. The films with thicknesses between 40 and 4000 A were deposited by electron‐beam evaporation using a single‐crystal high purity Gd3Ga5O12 source. Metal‐insulator‐semiconductor (MIS) and metal‐insulator‐metal structures (MIM) were fabricated in order to determine dielectric properties, which were found to depend strongly on deposition conditions such as substrate temperature and oxygen pressure. We obtained excellent dielectric properties for films deposited at substrate temperatures of 40 °C with no excess oxygen and at 125 °C with an oxygen partial pressure of 2×10−4 Torr. Specific resistivities ρ and dc breakdown fields Em of up to 6×1013 Ω cm and 2.1 MV/cm, respectively, were measured. Static dielectric constants between 9.93 and 10.2 were determined for these films. Like in other dielectrics, the current transport mechanisms are found to be bulk rather than electrode controlled.

Top‐surface emitting lasers with 1.9 V threshold voltage and the effect of spatial hole burning on their transverse mode operation and efficiencies

The fabrication and operating characteristics of a 1.9 V top surface emitting laser are presented. A planar fabrication process with a modified ion implantation mask is used to achieve gain guided lasers operating up to 90 °C. The laser operates in the fundamental mode up to 0.7 mW with 3.2 mW total peak optical output power. Direct evidence of spatial hole burning for the fundamental and the next higher mode is observed. This spatial hole burning puts a limit on the fundamental mode operation and efficiency of the lasers.

Giant enhancement of luminescence intensity in Er-doped Si/SiO2 resonant cavities

Si/SiO2 Fabry–Perot microcavities with rare‐earth‐doped SiO2 active regions are realized for the first time. Cavity‐quality factors exceeding Q=300 are achieved with structures consisting of two Si/SiO2 distributed Bragg reflectors and an Er‐implanted (λ/2) SiO2 active region. The room‐temperature photoluminescence intensity of the on‐axis emission is 1–2 orders of magnitude higher for resonant cavity structures as compared to structures without a cavity.

Enhanced spectral power density and reduced linewidth at 1.3 μm in an InGaAsP quantum well resonant-cavity light-emitting diode

The active region of an InGaAsP single‐quantum well light‐emitting diode (LED) emitting at 1.3 μm has been placed in the antinode of a resonant cavity consisting of a 32‐period distributed Bragg reflector (DBR) and a top silver mirror, with reflectivities of 92% and 95%, respectively. The dominant feature of the 300 K electroluminescence emission at all current levels is a 3 nm (2.8 meV) wide spontaneous emission peak centered on the cavity resonance wavelength. The spectral power density of the structure is more than one order of magnitude higher as compared to a structure without cavity. The resonant‐cavity LED operates without gain yet the extremely narrow spectrum indicates that the structure is suitable for wavelength division multiplexing applications.

Increased fiber communications bandwidth from a resonant cavity light emitting diode emitting at λ=940 nm

Substrate‐emitting InGaAs/AlGaAs resonant cavity light emitting diodes (RCLEDs) emitting at λ=940 nm have been fabricated for use in optical communications. The devices exhibit a high output efficiency, with a far‐field intensity of 85 μW/Steradian from a planar surface at a current of 14 mA. The spontaneous spectrum exhibits a very narrow peak of only 5 nm width, as opposed to the 50‐nm‐wide peak of an 875 nm wavelength reference LED. We show that the narrow spectrum drastically reduces the effects of chromatic dispersion within a 3.37 km length of 62.5 μm core graded index multimode fiber. The resulting −3 dB frequency is 102 MHz for the RCLED and fiber system, as opposed to only 33 MHz for the chromatic dispersion limited reference device.

Elimination of heterojunction band discontinuities by modulation doping

Heterojunction band discontinuities have been an active field of research during the last decade’ and made possible the realization of new device concepts such as modulation-doped transistors, heterobipolar transistors, and quantum-well lasers. The physical principles of these devices are based on heterojunction band discontinuities. In other device structures, however, heterojunction band discontinuities impede the flow of charge carriers across the junction. These structures include the optical distributed Bragg reflector which consists of alternating layers of two semiconductors with different refractive index, each having a thickness of a quarter wavelength. If distributed Bragg reflectors are used for current conduction, the constituent heterojunction band discontinuities impede the current flow, which is a highly undesired concomitant effect. It is the purpose of this publication to demonstrate that unipolar heterojunction band discontinuities can be eliminated by modulation doping and compositional grading of heterojunctions. The charge carrier transport across a heterojunction is illustrated in Fig. 1, which shows the band diagram of two semiconductors “A” and “B.” Band discontinuities occur in the conduction and valence band since the fundamental gap of semiconductor B is larger than the gap of A. Such discontinuities are usually referred to as type-1 heterojunctions, which contrast to type-11 (staggered) and type-III (broken gap) heterostructures. Transport across the heterojunction barrier can occur via thermal emission or via tunneling as schematically illustrated in Fig. 1. For sufficiently thick and high barriers, tunneling and thermal emission of carriers are not efficient transport mechanisms across the barrier. It is therefore desirable to eliminate such heterojunction band discontinuities in the conduction or valence band. Modulation doping of a parabolically graded heterojunction will next be shown to result in a flat-band-edge potential. The band diagram of a parabolically graded conduction-band edge is shown in Fig. 2 (a). The energy of the band edge increases parabolically with a positive second derivative between the points z, and z,. The band edge further increases parabolically with a negative second derivative between z2 and zs. The energy of the band edge can be expressed as / -&(z,) + 2(zf~z,)‘iz - zd’