There are many potential applications of visible, red (650nm - 690nm) vertical cavity surface emitting lasers (VCSELs)
including high speed (Gb) communications using plastic optical fiber (POF), laser mouse sensors, metrology, position
sensing. Uncertainty regarding the reliability of red VCSELs has long been perceived as the most significant roadblock
to their commercialization. In this paper we will present data on red VCSELs optimized for performance and reliability
that will allow exploitation of this class of VCSEL in a wide range of high volume consumer, communication and
VCSELs operating at ~665nm have been fabricated on 4" GaAs substrates using MOCVD as the growth process and
using standard VCSEL processing technology. The active region is AlGaInP-based and the DBR mirrors are made from
AlGaAs. Threshold currents are typically less than 2mA, the devices operate up to >60C and the light output is polarized
in a stable, linear characteristic over all normal operating conditions. The 3dB modulation bandwidth of the devices is in
excess of 3GHz and we have demonstrated the operation of a transceiver module operating at 1.25Gb/s over both SI-POF
Ageing experiments carried out using a matrix of current and temperature stress conditions allows us to estimate that the
time to failure of 1% of devices (TT1%F) is over 200,000h for reasonable use conditions - making these red VCSELs
ready for commercial exploitation in a variety of consumer-type applications. Experiments using appropriate pulsed
driving conditions have resulted in operation of 665nm VCSELs at a temperature of 85°C whilst still offering powers
useable for eye-safe free space and POF communications.
We present results on Resonant Cavity Light Emitting Diodes (RCLEDs) emitting at 650 nm, which have high efficiencies and low voltages. In particular, we report on the angular properties of these devices, and highlight the observation that overall spectral linewidth increases with collection angle. This unusual property of RCLEDs is largely a consequence of employing a microcavity in the design. An additional contributing factor is the relative distribution of gain amongst the cavity modes (i.e. the level of tuning or detuning of the underlying emission, defined with respect to the longitudinal cavity mode). We have used measurement techniques which spectrally resolve angular radiation profiles to determine the (de)tuning directly. Moreover, these profiles demonstrate how the overall spectral linewidth increases with collection angle. To this end, we have developed a semi- empirical method for determining the overall linewidth as a function of emission numerical aperture (NA). A 4 nm detuned device has been investigated and linewidths have been found to increase from 3.1 nm to 13.6 nm over a range of NA approximately equals 0 to NA equals 1, an increase by a factor of around 4. Obviously, a variable linewidth also implies a variable coherence length with NA. Consequently, the coherence length was found to decrease from 30 micrometer to 9 micrometer over the same range. Independent coherence length measurements were carried out by direct interferometric measurements, and confirmed the expected trends.
The essential elements of strain effects on the electronic structure of lnGa1As-(AlGa)As on GaAs are
elucidated. Attention is focused on the optical properties of quantum wells and superlattices(SL) with In
fractions <0.12. Photoluminescence and photoluminescence excitation spectroscopy at '-4K has revealed
sharp exciton features and allowed us to measure the el-hhl binding energy versus well width, identify
Ln =0 and transitions and follow the development of SL minibands. Comparison with envelope function
calculations suggests the band offset ratio remains constant (67:33) up to x=O.12.