T. D. Osentowski

Very high‐efficiency semiconductor wafer‐bonded transparent‐substrate (AlxGa1−x)0.5In0.5P/GaP light‐emitting diodes

Data are presented demonstrating the operation of transparent‐substrate (TS) (AlxGa1−x)0.5In0.5P/GaP light‐emitting diodes (LEDs) whose efficiency exceeds that afforded by all other current LED technologies in the green to red (560–630 nm) spectral regime. A maximum luminous efficiency of 41.5 lm/W (93.2 lm/A) is realized at λ∼604 nm (20 mA, direct current). The TS (AlxGa1−x)0.5In0.5P/GaP LEDs are fabricated by selectively removing the absorbing n‐type GaAs substrate of a p‐n (AlxGa1−x)0.5In0.5P double heterostructure LED and wafer bonding a ‘‘transparent’’ n‐GaP substrate in its place. The resulting TS (AlxGa1−x)0.5In0.5P/GaP LED lamps exhibit a twofold improvement in light output compared to absorbing‐substrate (AS) (AlxGa1−x)0.5In0.5P/GaAs lamps.

HIGH PERFORMANCE ALGAINP VISIBLE LIGHT-EMITTING DIODES

The performance of surface‐emitting visible AlGaInP light‐emitting diodes (LEDs) is described. The devices have external quantum efficiencies greater than 2% and luminous efficiencies of 20 lm/A in the yellow (590 nm) spectral region. This performance is roughly ten times better than existing yellow LEDs and is comparable to the highest performance red AlGaAs LEDs currently available. The devices also perform favorably compared to existing devices in the orange and green spectral regions. Low‐pressure organometallic vapor phase epitaxy (OMVPE) is used to grow the epitaxial layers. The devices consist of a double heterostructure with an AlGaInP active region grown on a GaAs substrate.

Twofold efficiency improvement in high performance AlGaInP light-emitting diodes in the 555-620 nm spectral region using a thick GaP window layer

AlGaInP light‐emitting diodes (LEDs) with external quantum efficiencies ≥6% and luminous performance of 20 lm/W have been fabricated. These LEDs are twice as efficient as previously reported AlGaInP devices throughout the spectral region from green (555 nm) to red‐orange (620 nm) owing to a thicker GaP window layer (45 vs 15 μm). Using hydride vapor phase epitaxy, thick GaP window layers were grown on top of AlGaInP double heterostructures grown by organometallic vapor phase epitaxy. The efficiency of the LEDs was found to improve as the thickness of the window layer was increased from 9 to 63 μm. This improvement is predicted by a simple model that considers the benefit of enhanced emission through the sides of the thick window. The effect of emission wavelength on quantum efficiency and luminous performance for AlGaInP LEDs with a 45 μm thick window has been studied.

Properties and use on In 0.5 (Al x Ga 1-x ) 0.5 P and Al x Ga 1-x As native oxides in heterostructure lasers

Data are presented demonstrating the formation of native oxides from high Al composition In0.5(AlxGa1-x)0.5P (x≳ 0.9) by simple annealing in a “wet” ambient. The oxidation occurs by reaction of the high Al composition crystal with H2O vapor (in a N2 carrier gas) at elevated temperatures (≥500° C) and results in stable transparent oxides. Secondary ion mass spectrometry (SIMS) as well as scanning and transmission electron microscopy (SEM and TEM) are employed to evaluate the oxide properties, composition, and oxide-semiconductor interface. The properties of native oxides of the In0.5(AlxGa1-x)0.5P system are compared to those of the AlxGa1-xAs system. Possible reaction mechanisms and oxidation kinetics are considered. The In0.5(AlxGa1-x)0.5P native oxide is shown to be of sufficient quality to be employed in the fabrication of stripe-geometry In0.5(AlxGa1-x)0.5P visible-spectrum laser diodes.

Impurity‐induced layer disordering of high gap Iny(AlxGa1−x)1−yP heterostructures

Data are presented showing the impurity‐induced layer disordering (IILD), via low‐temperature (600–675 °C) Zn diffusion, of In0.5(AlxGa1−x)0.5P quantum well heterostructures and an In0.5Al0.2Ga0.3P‐GaAs heterojunction grown using metalorganic chemical vapor deposition. Secondary ion mass spectroscopy, transmission electron microscopy, and photoluminescence are used to confirm IILD, which occurs via atom intermixing on the column III site aided by column‐III‐atom interstitials. In addition, high‐temperature anneals (800–850 °C) are performed on the same crystals to confirm the thermal stability of the heterointerfaces.

Native‐oxide stripe‐geometry In0.5(AlxGa1−x)0.5P‐In0.5Ga0.5P heterostructure laser diodes

Data are presented demonstrating the formation of stable, device‐quality native oxides from high Al composition In0.5(AlxGa1−x)0.5P (x ∼0.9) via reaction with H2O vapor (in N2 carrier gas) at elevated temperatures (≥500 °C). The oxide exhibits excellent current‐blocking characteristics and is employed to fabricate continuous room‐temperature stripe‐geometry In0.5(AlxGa1−x)0.5P‐In0.5Ga0.5P double‐heterostructure laser diodes.

Impurity‐induced layer disordering in In0.5(Alx Ga1−x)0.5P‐InGaP quantum‐well heterostructures: Visible‐spectrum‐buried heterostructure lasers

Diffusion of Si into quantum‐well heterostructures and superlattices employing the high gap III‐V quaternary system Iny (AlxGa1−x )1−yP is shown to result in impurity‐induced layer disordering. Secondary ion mass spectroscopy, transmission electron microscopy, and photoluminescence data indicate that the diffusion of Si into an InAlP‐InGaP superlattice grown lattice matched on GaAs (y≊0.5) results in the intermixing of the layers, thus forming an alloy of average composition. Buried‐heterostructure lasers are fabricated using Si layer disordering of In0.5 (Alx Ga1−x )0.5 P p‐n quantum‐well heterostructures. The disorder‐defined stripe‐geometry diode lasers operate pulsed at 300 K near 6400 A. Continuous wave operation at λ∼6255 A is achieved at −47 °C.

Short‐wavelength (∼625 nm) room‐temperature continuous laser operation of In0.5(AlxGa1−x)0.5P quantum well heterostructures

Data are presented demonstrating very‐short‐wavelength (625 nm) room‐temperature (300 K) continuous (cw) photopumped laser operation of In1−y(AlxGa1−x)yP‐In1−y (AlxGa1−x)yP quantum well heterostructures grown lattice matched (y≊0.5) on a GaAs substrate via metalorganic chemical vapor deposition. In addition, 300 K pulsed laser operation (Jth∼104 A/cm2, 625 nm) of diodes fabricated from the same crystal is described.

Stimulated emission in In0.5(AlxGa1−x)0.5P quantum well heterostructures

For shorter wavelength lasers (λ<6000 nm), the most prospective III–V alloy system is In1−yGayP lattice matched to GaAs (y∼0.5) and its variant, the case of AlGa substitution, In0.5(AlxGa1−x)0.5P. We report the growth of quantum well heterostructures (QWHs) in this system by metalorganic vapor phase epitaxy and the photopumped (77 K) laser operation of InAlGaP QWHs at wavelengths ranging from the orange to the green portions of the spectrum. Continuous wave (CW) photopumped laser operation at 77 K is achieved in the range from ∼5570.0 to ∼550.0 nm (2.175 to 2.25 eV), and pulsed operation to wavelenghts as short as 543.0 nm (2.283 eV). Room temperature pulsed laser operation is demonstrated in the range from ∼610.0 to 590.0 nm (2.032 to 2.101 eV). The shortest lasing wavelengths observed at 77 K (543.0 nm pulsed and 553.0 nm CW) and at 300 K (593.0 nm pulsed and 625.0 nm CW) represent the highest energy lasers yet reported for this material system, or for any III–V alloy system. This paper will describe the epitaxial layers grown, the characterization of these layers using a variety of techniques, including TEM, and the laser operation experiments and results.

Planar native‐oxide buried‐mesa AlxGa1−xAs‐In0.5(AlyGa1−y)0.5P‐ In0.5(AlzGa1−z)0.5P visible‐spectrum laser diodes

Data are presented demonstrating the continuous (cw) room‐temperature (23 °C) operation of planar index‐guided ‘‘buried‐mesa’’ AlxGa1−xAs‐In0.5(AlyGa1−y)0.5P‐ In0.5Ga0.5P heterostructure visible‐spectrum laser diodes. The planar ‘‘mesa’’ structure is formed by ‘‘wet’’ oxidation (H2O vapor+N2 carrier gas, 550 °C) of the AlxGa1−xAs on the composite AlxGa1−xAs‐In0.5(AlyGa1−y)0.5P upper confining layer (outside of the active stripes). The oxidation process results in a ∼0.5‐μm‐thick native oxide located (in depth) within ∼3000 A of the active layer in the region outside of the laser stripes themselves. The oxide possesses excellent current‐confinement properties and a low refractive index (n≊1.60), resulting in relatively low‐threshold laser operation for narrow‐stripe devices. In addition, these devices exhibit transverse‐mode confinement and small beam astigmatism because of the refractive index step provided by the deep native oxide.