Shigeru Nakagawa

Determination of piezoelectric fields in strained GaInN quantum wells using the quantum-confined Stark effect

We have identified piezoelectric fields in strained GaInN/GaN quantum well p-i-n structures using the quantum-confined Stark effect. The photoluminescence peak of the quantum wells showed a blueshift with increasing applied reverse voltages. This blueshift is due to the cancellation of the piezoelectric field by the reverse bias field. We determined that the piezoelectric field points from the growth surface to the substrate and its magnitude is 1.2 MV/cm for Ga0.84In0.16N/GaN quantum wells on sapphire substrate. In addition, from the direction of the field, the growth orientation of our nitride epilayers can be determined to be (0001), corresponding to the Ga face.

Second‐harmonic generation from GaAs/AlAs vertical cavity

We have demonstrated second‐harmonic generation in a GaAs/AlAs vertical cavity grown on a (311)B GaAs substrate. Second‐harmonic light of 492 nm was observed and its efficiency was measured to be 1.4×10−4 %/W. The cavity confines high intensity of fundamental field, resulting in efficient second‐harmonic generation. Quasiphase matching was realized with the stacked GaAs/AlAs layers inside the cavity, which was designed taking into account the strong absorption of second‐harmonic power in GaAs layers. We show that conversion efficiency of the GaAs/AlAs vertical cavity could be more than 10%/W if the optimization is completed.

Blue vertical-cavity surface-emitting lasers based on second-harmonic generation grown on (311)B and (411)A GaAs substrates

We have studied blue vertical-cavity surface-emitting lasers (VCSELs) based on second-harmonic generation (SHG) grown on (411)A and (311)B GaAs substrates in order to investigate suitable substrate orientations for SHG-VCSELs. The comparison among substrate orientations has been made on three parameters, SHG conversion efficiency, transparency current density and gain coefficient. The transparency current density and the gain coefficient are characterized by edge emitting lasers grown on the above substrates. We also discuss the transparency current density and the gain coefficient for (311)A reported previously by Takahashi et al. [M. Takahashi, M. Hirai, K. Fujita, N. Egami, and K. Iga, J. Appl. Phys. 82, 4551 (1997)]. SHG conversion efficiency is 38 and 30% W for SHG-VCSELs grown on (311)B and (411)A substrates, respectively, which is consistent with theory, assuming identical nonlinear coefficients for the A face and B face. Transparency current density for (311)A, (311)B and (411)A is 80, 105 and 60 ...

Second-harmonic generation in vertical-cavity surface-emitting laser

A concept for a short-wavelength compact laser is proposed, in which second-harmonic coherent light is produced by converting fundamental light lased in a vertical-cavity surface-emitting laser. A layer is incorporated inside the laser cavity particularly for efficient second-harmonic generation. This layer consists of second-order optical nonlinear crystals which are preferably III–V- or II–VI-system compound semiconductors epitaxially grown with crystal orientation tilted from . Simulation indicates that the device will produce several hundred µ W with AlAs/GaAs alternating layers for second-harmonic generation and an InGaAs active layer for lasing.

Continuous‐wave operation of a blue vertical‐cavity surface‐emitting laser based on second‐harmonic generation

An InGaAs/GaAs vertical‐cavity surface‐emitting laser has been fabricated on a (311)B GaAs substrate. Pulsed lasing operation is obtained at room temperature, and continuous‐wave lasing operation is obtained at less than 270 K. From the device, blue laser emission based on second‐harmonic generation is observed. The wavelength of the blue laser emission is 482 nm. At 135 K, its output power is 1 nW under continuous‐wave operation and more than 10 nW under pulsed operation.

Quantum-confined Stark effect in strained GaInN quantum wells on sapphire (0 0 0 1)

We have studied the quantum-confined Stark effect in strained GaInN/GaN quantum wells p-i-n structure on sapphire (0001) by using room temperature photoluminescence measurements with applied voltages. The photoluminescence peak in GaInN/GaN quantum wells was blue-shifted by increasing the applied reverse voltage. This is due to the cancellation of the piezoelectric field by the reverse bias. This piezoelectric field pointed from the growth surface to the substrate, and its magnitude was determined to be 1.3 MV/cm in strained Ga 0.84 In 0.16 N layers.

Vertical-Cavity Surface-Emitting Lasers with Stable Polarization Grown on (411)A-Oriented GaAs Substrates

We demonstrate continuous-wave operation at room temperature for vertical-cavity surface-emitting lasers (VCSELs) grown on (411)A-oriented GaAs substrates by molecular beam epitaxy. A threshold current of 0.5 mA is obtained for selectively oxidized VCSELs with a square-shaped emitting aperture of 4×4 µm2. The polarization is well stabilized parallel to the [\overline122] direction that has the highest optical gain.

Second-Harmonic Generation from GaP/AlP Multilayers on GaP(111)Substrates Based on Quasi-Phase Matching for the Fundamental Standing Wave

We have demonstrated second-harmonic generation (SHG) from GaP/AlP multilayers on GaP(111)A substrates based on quasi-phase matching (QPM) for the fundamental standing wave. Theoretical calculation predicted that the SHG power increases with increasing number of GaP/AlP multilayers because of their small absorption coefficient in the spectral range of second-harmonic light, which is in contrast to the case of GaAs/AlAs QPM multilayers. In the transmission SHG measurement using a frequency-tunable Ti:Sapphire laser as a fundamental wave source, maximum SHG power was obtained at a fundamental wavelength of 990 nm from the five-pair GaP/AlP QPM multilayers. The wavelength conversion efficiency was measured to be 9.8×10-10%/W, which was smaller than the theoretical value of 6.5×10-8%/W.

Growth of vertical cavity surface emitting laser material on (3 1 1)B GaAs by MBE

We report on the growth of VCSEL structures on (3 1 1)B GaAs substrates. For the growth of AlGaAs and AlAs, the best morphology and material quality were obtained for growth temperatures > 650°C. Surface morphology and mirror reflectivity degraded significantly at low growth temperatures ( < 600°C). From low-temperature photoluminescence (LTPL), we found a forbidden temperature range for the growth of InGaAs quantum well-active regions on (3 1 1)B substrates between 540 and 560°C. Active region growth temperatures in this range showed low intensity, broad LTPL, and poor laser characteristics. Cross-section TEM measurements show poor homogeneity for material grown in this temperature range. At higher temperatures (580°C), In desorption is greatly increased, so < 520°C was selected as the optimal growth temperature. Even with a non-optimized structure, the first reported VCSELs on (3 1 1)B were fabricated with a pulsed J th = 9 kA/cm 2 at - 40°C and 28 kA/cm 2 at room temperature. At - 40°C, 10 nW of SHG blue light at 485 nm was detected under pulsed conditions, and 2 nW was detected under CW conditions and was visible to the naked eye. By improving the structure we obtained CW lasing at room temperature with 300 A/cm 2 as a broad area laser and 1.4 kA/cm 2 as a VCSEL. A maximum power of 0.55 nW at 490 nm was detected CW at room temperature.