N. Yokouchi

40 AA continuous tuning of a GaInAsP/InP vertical-cavity surface-emitting laser using an external mirror

Continuous tuning of 40 AA was achieved in a GaInAsP/InP vertical-cavity surface-emitting laser for the first time. The cavity length was directly changed by slightly moving an external mirror. The device was grown by chemical beam epitaxy (CBE) and the experiment was performed at low temperature. The result indicates that a short cavity structure can provide pure continuous wavelength tuning because of its wide longitudinal mode spacing.<<ETX>>

Surface emitting lasers grown by chemical beam epitaxy

Abstract We have established a chemical beam epitaxy technology for the growth of λ = 1.55 μm GaInAsP/InP surface emitting laser wafers by confirming the controllability of composition and thickness, and doping conditions. We investigated the optical and electrical properties of Be-doped InP, necessary for obtaining good surface morphology and low electrical resistance. The crystal quality was characterized by making stripe lasers, and the growth of GaInAsP/InP multilayer reflectors was attempted. Also, the first lasing of 1.5 μm surface emitting lasers has been demonstrated by chemical beam epitaxy (CBE) and a very low threshold was realized using a hybrid mirror.

Some optical characteristics of beryllium-doped InP grown by chemical beam epitaxy (CBE)

Abstract Beryllium-doped InP was grown by chemical beam epitaxy to investigate its doping and optical characteristics Hole concentration as high as 1 × 10 19 cm −3 was obtained with mirror-like surface morphology, while maintaining a growth temperature of 500°C and a growth rate of 1.5 μm/h. The room temperature photoluminescence intensity of highly doped InP up to 1 × 10 19 cm −3 was not deteriorated compared with undoped InP. We also found that the spectral linewidth broadened and peak wavelength shifted to the long wavelength side with increasing hole concentrations. These phenomena can be explained by the band-to-band transition and the beryllium-related band-to-acceptor level emission.

CBE grown 1.5 mu m GaInAsP-InP surface emitting lasers

GaInAsP-InP surface-emitting (SE) lasers have been fabricated using chemical beam epitaxy (CBE) and their lasing characteristics investigated. A threshold current of 2.6 mA was obtained under 77 K CW operation for a device with an improved GaInAsP contact layer having 0.1- mu m thickness and relatively low hole concentration (1x10/sup 19/ cm/sup -3/) to reduce the optical loss. A hybrid mirror consisting of a semiconductor distributed Bragg reflector (DBR) and Si-SiO/sub 2/ multilayers is introduced. Threshold current as low as 1.7 mA was obtained at 77 K CW operation, the lowest values at 77 K for long-wavelength SE lasers ever reported. Near-room-temperature pulsed operation was also obtained for both structures. >

Photoluminescence characterization of GaxIn1−xAs (0 ≤ x ≤ 0.32) strained quantum wells grown on InP by chemical beam epitaxy

Abstract We have investigated some characteristics of GaxIn1−xAs/InP (x = 0, 0.2, 0.32) strained materials by growing multi-quantum wells with various well widths from 3 to 60 A by chemical beam epitaxy. Growth conditions such as valve sequences and growth interruptions were optimised to have single-peaked photoluminescence spectra for all strained samples. Measured room temperature emission wavelengths were compared with theoretically estimated values. Photoluminescence linewidths were around 16 meV for most samples at 77 K, but broadened for well widths of less than 20 A. Photoluminescence intensity also peaked at well width of 20 A for all compositions. Performances of optical devices may be closely related to this “critical thickness” determined probably by the growth system limitation.

Ultra-thin Ga x In 1-x As/InP (0 ≤ x ≤ 0.47) layer growth by chemical beam epitaxy

GaxIn1−xAs/InP (0≤x≤0.47) lattice-matched and compressively strained quantum wells were grown by all gas source chemical beam epitaxy (CBE). Their optical properties were investigated by photoluminescence (PL) and optical absorption measurements. The thinnest GaxIn1−xAs layer was 6Å-thick (2 monolayers) for Ga0.47In0.53As and 3Å-thick (1 monolayer) for InAs. In PL measurements, we found that for strained materials (x<0.47) luminescence intensity dropped with decreasing barrier thickness. Optical absorption properties were measured at room temperature, and excitonic absorption peaks were clearly observed. The wavelengths of excitonic peaks were in good agreement with a theoretical estimation obtained by using an effective mass approximation including heavy and light hole energy splitting at the γ point.

Band discontinuity reduction of i-GaInAsP/p-InP for improving 1.55 /spl mu/m GaInAsP/InP surface emitting laser performances

The long wavelength GaInAsP/InP surface emitting (SE) laser is becoming important for use in optical fiber networks. We reported a low threshold GaInAsP/InP SE laser grown by chemical beam epitaxy (CBE) with some device characteristics. However, its temperature dependence on threshold and efficiency are inferior to those of short wavelength SE lasers. The auger process and intervalence band absorption were discussed as the primary causes of the worse temperature characteristic. In addition to these, the potential spike at the active layer and p-cladding hetero-interface may require an additional voltage bias to inject holes. Takemoto et al. proposed a band discontinuity reduction (BDR) layer to reduce the spike height. Kazarinov et al. Pointed out that this spike reduces a potential barrier for electron confinement in the active layer and increases an electron overflow to the p-cladding layer. A preliminary calculation shows the carrier overflow may degrade the performance of long wavelength SE lasers. In this study, we investigate the current-voltage characteristic of the hetero-interface and introduce a BDR layer which has an intermediate composition between the active layer and the p-cladding layer in order to improve the temperature characteristic of long wavelength SE lasers.<<ETX>>

Composition changes in GaxIn1−xAs/InP superlattice growth by chemical beam epitaxy

Abstract The variation of compositions in ultra-thin Ga x In 1− x As/InP layers grown by chemical beam epitaxy (CBE) was investigated. The Ga atomic content of the grown Ga x In 1− x As was evaluated by an X-ray diffraction method. By comparing with theoretical simulation, we found a lack of Ga content in very thin layer growth. The reduction of Ga content ranged from 0.47 to 0.33 for 4-monolayer superlattice. Our result implies that there are some transition layers at the beginning of Ga x In 1− x As growth which should be eliminated.

Growth of GaInAs(P)/InP multi-quantum barrier by chemical beam epitaxy

Abstract A multi-quantum barrier (MQB) using the GaInAsP/InP system has been demonstrated for the first time. Some n-i-n tunneling diodes consisting of MQBs and bulk barriers were grown by chemical beam epitaxy (CBE). From the measurement of 77 K current-voltage ( I – V ) characteristics, we have confirmed the carrier confinement effect by the MQB. Moreover, by measuring of the excitation power dependence of the photoluminescence (PL) peak intensity at room temperature, it was obtained that the intensity of the sample with MQB was about 3 times greater than that with a bulk barrier. From the measurement of PL peak intensity and I – V characteristics of an n-i-n tunneling diode, we have experimentally verified the effect of electron wave rejection of a GaInAs(P)/InP MQB.

GaInAs/InP MQW and DBR growth for surface emitting lasers by CBE

Abstract Growth rates of 1 to 6 μm/h were obtained for Ga 0.47 In 0.53 As using all gas-source chemical beam epitaxy. Using these high growth rates, quantum wells and distributed Bragg reflectors were grown to study thickness controllability and material quality. Growth rate linearity of GaInAs was observed from growth times of 2 s to 1 h. The photoluminescence linewidth of 29 meV was obtained for 38 A wells at room temperature. We also investigated doping with Si and Be at high growth rates; as high as 2×10 20 cm -3 of Be doping in GaInAs was obtained. Finally, using high Si-doped GaInAs and InP, a multi-layered Bragg reflector was grown yielding 85% reflectivity at a wavelength of 1.6 μm.