Hideto Sugawara

Room‐temperature cw operation of InGaP/InGaAlP visible light laser diodes on GaAs substrates grown by metalorganic chemical vapor deposition

Room‐temperature cw operation for InGaP/InGaAlP double heterostructure (DH) laser diodes on GaAs substrates was achieved for the first time. The DH wafers were grown by low‐pressure metalorganic chemical vapor deposition using methyl metalorganics. A lasing wavelength of 679 nm and a threshold current of 109 mA at 24 °C were obtained for an inner stripe structure laser diode with a 250‐μm‐long and 7‐μm stripe geometry. The laser operated at up to 51 °C. The characteristic temperature T0 was 87 K at around room temperature. The lowest threshold current density, 5.0 kA/cm2, was obtained with a 20‐μm stripe width laser diode under room‐temperature pulsed operation.

Growth of high-quality inGaAIP epilayers by MOCVD using methyl metalorganics and their application to visible semiconductors lasers

In an attempt to obtain high-quality In0.5(Ga1−xA1x) 0.5P epilayers on GaAs substrates for visible semiconductor la applications, effects of growth procedure and conditions (growth temperature, V/III ratio, etc.) were investigated by low-pressure MOCVD technique, using trimethyl metalorganics. It was found that fast gas compositional switching, growth temperatures as high as 700°C and V/III ratios larger than 200 were prerequisite to obtaining high-quality epilayers. Low-resistivity layers with resistivity less than 0.2 Ω cm were readily obtained with both Se and Zn doping for x<0.5. Room temperature CW operation of an In0.5Ga0.5P/In0.25A10.25P DH laser was achieved, with a threshold current density of 5.0 kA/cm2, using DH wafers grown under optimized growth conditions.

High‐efficiency InGaAlP/GaAs visible light‐emitting diodes

High‐efficiency InGaAlP surface emission light emitting diodes (LEDs) have been successfully fabricated. Newly designed double‐heterostructure LEDs with a GaAlAs current spreading layer were employed to expand the light emission area, which is necessary to take out the light efficiently. The external quantum efficiency was 1.5% at 620 nm orange light for an In0.5 (Ga0.8Al0.2)0.5P active layer LED. This LED is five times more efficient at 620 nm than that of the GaAlAs and GaAsP LEDs. 563 nm green electroluminescence, which is the shortest wavelength ever reported for InGaAlP LEDs, was also achieved with an In0.5(Ga0.5Al0.5)0.5P active layer.

High‐brightness InGaAlP green light‐emitting diodes

Candela class InGaAlP surface‐emission green light‐emitting diodes (LEDs) have been successfully fabricated. The growth of InGaAlP on an intentionally misoriented substrate improved emission properties, as confirmed by a quantitative estimation of the diffusion length in the active material. A Bragg reflector using InGaAlP was realized for the first time. A new device structure, including this Bragg reflector, drastically improved the light extraction efficiency. An external quantum efficiency of 0.7% at 573 nm green light was obtained, corresponding to a luminous intensity of 2 cd.

Growth temperature dependent atomic arrangements and their role on band-gap of InGaAlP alloys grown by MOCVD

Detailed observation of atomic arrangement in In0.5(Ga1−xAlx)0.5P(0⩽x⩽1) grown by MOCVD with a wide range of growth temperatures Tg (570–770° C) was carried out using electron diffraction and high resolution transmission electron microscopy. A correlation between the atomic arrangement and band-gap energy was studied by photoluminescence and photoacoustic spectroscopy. For Tg≲760° C, the epitaxial layers have ordered structures. For Tg≳770° C, the ordering disappear. Shifts in the band-gap depend on the density of the ordered layers for x≲0.5. For x≳0.5, the band-gap is not affected by the ordering.

A study of p-type doping for AlGaInP grown by low-pressure MOCVD

Abstract Doping characteristics for Mg (and Zn) in (Al x Ga 1− x ) 0.5 In 0.5 P have been studied with a view towards applying Mg (or Zn) doped AlInP to DH lasers. The solubility limits for the dopants decreased with increasing Al composition. The maximum hole concentration of Zn doped AlInP was at most 2×10 17 cm −3 , which is too low for practical use in DH lasers. The solubility limits for Mg were several times higher than those for Zn. The maximum hole concentration of Mg doped AlInP was 1×10 18 cm −3 . The Mg incorporation was considered to be limited by Mg revaporization from the growth surface. The Mg incorpolation at a constant doping-source introduction in AlGaInP increased with increasing Al composition. The proportion of electrically active Mg to total incorpolated Mg (electrical activity) does not change markedly with Al composition. The Mg electrical activity was quite low even at low doping levels.

Characteristics of a distributed Bragg reflector for the visible‐light spectral region using InGaAlP and GaAs: Comparison of transparent‐ and loss‐type structures

Distributed Bragg reflectors (DBRs) for the visible‐light spectral region constructed by InAlP/InGaAlP pairs and InAlP/GaAs pairs, grown by metalorganic chemical‐vapor deposition, have been investigated with the point of comparing optical and structural properties. In the case of the InAlP/InGaAlP stacked type, a reflectivity above 80% has been realized; however, the bandwidth decreased by shortening the peak wavelength. The reflection spectrum of the InAlP/GaAs DBR showed a wide‐band characteristic and provided a relatively high reflectivity to the green region in spite of the absorption loss of the GaAs layers. These results were in good agreement with theoretical calculations considering the absorption loss and refractive index of individual stacked layers. These DBRs have also been confirmed to have good uniformity and periodicity through cross‐sectional transmission electron microscopy and x‐ray rocking curve analysis. Good electrical conductivity through these DBRs has been obtained for the n‐type s...

Hybrid-Type InGaAlP/GaAs Distributed Bragg Reflectors for InGaAlP Light-Emitting Diodes

Hybrid-type distributed Bragg reflectors (DBRs) with InAlP/GaAs and InAlP/InGaAlP multilayers grown by metalorganic chemical vapor deposition (MOCVD) have been investigated. The structure of the DBRs was designed using a theoretical calculations considering the absorption loss and refractive index of each stacked layer. The wide-band, high-reflectivity characteristics were also experimentally confirmed. Good electrical conductivity through InGaAlP light-emitting diodes (LEDs) with the hybrid-type DBRs was obtained in spite of the many interface needed for the multiple layers of the DBRs. A luminous intensity of 0.8 cd was obtained at 565.7 nm (nearly pure green light).

Reduction of residual oxygen incorporation and deep levels by substrate misorientation in InGaAlP alloys

Effects of substrate misorientation on deep levels and on oxygen incorporation have been investigated in undoped In0.5(Ga1−xAlx)0.5P(x = 0.0−1.0) grown be metalorganic chemical vapor deposition (MOCVD). Deep-level transient spectroscopy (DLTS) measurements have revealed three deep levels (EDLTS = 0.42 eV, 0.64 eV and ≈ 1.0 eV). The concentrations of the deeper two deep levels increased with increasing x, and they were drastically reduced by using (100) substrate 15° off tilted towards [011]. The residual oxygen concentration was also reduced by using the off-axis substrate. It has been shown that the above-mentioned two deep levels are related to oxygen, and have deterious effects on the luminescent properties of InGaAlP alloys.

Emission Properties of InGaAlP Visible Light-Emitting Diodes Employing a Multiquantum-Well Active Layer

Visible InGaAlP light-emitting diodes (LEDs) employing a multiquantum-well (MQW) active layer have been investigated. Photo luminescence measurements showed that growth on a GaAs substrate, with an intentional surface misorientation from the (100) plane towards the [011] direction, resulted in a marked improvement in the quality of the MQW compared with growth on a just (100) substrate. The emission properties of the LED strongly depended on the various parameters of the MQW structure, in particular the number of wells. The external quantum efficiency of a 600 nm LED with a 20-well MQW active layer was found to be 1.6%. The emission wavelength could be further reduced by 10 nm without any significant decrease in the external quantum efficiency.