We present a polarization sensitive device showing an adjustable bistable switching behavior. It exhibits switching contrasts of up to 30 dB, electrooptical gains of 40 dB, and an angle hysteresis which can be tuned between 0/spl deg/ and 60/spl deg/. Furthermore, the polarization characteristics are independent of the incident optical power.

The polarization anisotropy of ordered GaInP has been studied in electroluminescence and electroabsorption and has been applied to some optoelectronic device structures, operating at . Surface-emitting light emitting diodes (LEDs) have been fabricated which show a polarized light output. A contrast ratio of up to 2.0 dB has been observed between light emission which is linearly polarized along the and crystal directions, respectively. In the electroabsorption, an ordering-induced shift of the Franz-Keldysh spectra of up to 13 meV has been observed. This has been used to change the transmitted light intensity ratio between and polarized light from 0.2 to 2.8 dB by applying an electric field of . We have applied this polarization anisotropy of the absorption coefficient to realize polarization detectors, polarization threshold switches and polarization photo-transistors with a switching contrast of about 25 dB and sensitivities of about .

Summary form only given. We show that the strong polarization anisotropy of the absorption coefficient of ordered GaInP can be exploited to realize polarization-sensitive threshold switches. The photoconductive switch is basically a p-i-n photodiode and a field effect transistor integrated into a single device. Its principle is based on the light-induced increase of the n-layer conductance. First results show a switching contrast of 50 dB and a maximum sensitivity of /spl sim/ 3 dB/degree.

We have studied the polarization dependence of the absorption, electroabsorption (Franz-Keldysh effect) and electroluminescence of double hetero p-i-n structures based on ordered GaInP. An ordering induced shift of the Franz-Keldysh spectra of up to 12meV has been observed between the electroabsorption spectra for light polarized parallel to the [011] and [01-1] crystal direction, respectively. These measurements allow to get useful information about the valence band structure, like valence band splitting and band gap reduction. Moreover, the polarization dependence can also be utilized for polarization sensitive optoelectronic devices.Based on the strong polarization anisotropy of the absorption coefficient, a polarization threshold switch with an high photoconductive gain can be realized. This device shows a switching contrast of almost 50 dB and a maximum sensitivity of about 3 dB/degree. Light emitting diodes with ordered GaInP in the active region show a polarized light output. Depending on the ordering parameter a contrast ratio of up to 2.0 dB has been observed between the [011] and [01-1] polarized part of the emitted light.

Ordered GaInP shows a strong polarization anisotropy of the Franz–Keldysh absorption. Polarization-dependent electroabsorption measurements provide a powerful tool to obtain information about the valence band structure of ordered material. The measured polarization shift of the Franz–Keldysh spectra depends on the ordering parameter but is always smaller than the valence band splitting. By using a simple theory, one can extract the valence band splitting from the Franz–Keldysh data. In addition, the measured spectra allow a precise determination of the split-off energy.

We have investigated the electroabsorption due to the Franz–Keldysh effect in GaInP/AlGaInP p-i-n double heterostructures grown by metalorganic vapor phase epitaxy. The simultaneous evaluation of transmission and photocurrent measurements allowed an accurate determination of the field dependent absorption coefficient of ordered and disordered GaInP alloys. For ordered and disordered material, similar changes of the absorption coefficient as high as 4000 cm−1 have been observed for field changes of ΔE=250 kV/cm. Thermally disordered samples, however, showed a degradation of the electrical and optical properties.

The material system (Al) GaInP is very interesting for opto-electronic devices in the visible spectral range. Under suitable growth conditions (Al)GaInP epitaxial layers show a spontaneous self ordering of the CuPt B -type [1]. For growth in the [100]-direction this ordering results in alternating Ga-rich and In-rich {111} B planes. The mono-atomic superlattice causes significant changes of the electronic structure compared to the normal disordered alloy. In particular, ordered crystals exhibit a band gap reduction and a valence band splitting at the T-point. As a consequence of dipole selection rules, transitions between the highest valence band and the conduction band are forbidden for light polarized parallel to the ordering direction. This leads to a strong polarization anisotropy even for light propagating normal to the {100} crystal surface.

The polarization dependence of the Franz–Keldysh effect (FKE) in metalorganic vapor phase epitaxially grown AlGaInP/GaInP/AlGaInP p-i-n double heterostructures was investigated for samples with different ordering parameters. We determine an ordering induced shift of the FK spectra of up to 13 meV between light polarized along the [011] and [01-1] crystal directions. Due to the FKE the transmitted light intensity ratio between the respective polarizations was changed from 0.2 to 2.8 dB by applying an electric field of 335 kV/cm.

Under certain growth conditions GalnP tends to exhibit spontaneous superlattice ordering with atoms arranging in GaP/lnP monolayers along two of the possible four [111] crystal directions. The superlattice ordering leads to significant changes in the electrical and optical properties of the crystal most prominently decreasing the energy band gap. In ordered material optical transitions between the highest valence band and the conduction band are not allowed for polarisation parallel to the ordering directions. In order to demonstrate the potential device applications of this polarisation effect we have studied the electroluminescence (EL) and the electroabsorption of (Al0.3Ga0.7)0.52In0 48/Ga0 52ln0.48P p-i-n double hetero structures. Samples with ordered (o-samples) and disordered (d-samples) GalnP active layers have been grown lattice matched to GaAs by metal organic vapour phase epitaxy (MOVPE). The o-samples were grown at 650°C on exactly oriented GaAs substrates while for the d-samples a growth temperature of 710°C and 6° toward [111A] tilted substrates have been used. Moreover, thermal disordering of the o- samples was achieved by rapid thermal annealing (RTA) at 900°C for 30 sec after growth (a-samples). This technique allows to compare ordered and disordered material made from the same epitaxial wafer. Surface emitting light emitting diodes (LED) with chemically dry etched mesas have been fabricated. The EL spectra of o- and a-LED show peaks at 673 nm and 650 nm respectively. This corresponds to an energy shift of 65 meV and is in very good agreement with PL measurements. The a-samples exhibit a significantly decreased EL-efficiency compared to the o-LED which can be explained by damage caused by RTA. Polarisation measurements of o-LEDs exhibit a contrast of 1.4 dB between polarisation parallel to the [ 01 1 ¯ ] and [011] crystal direction respectively. This effect is nearly independent of diode current and mesa geometry, but not observed for a-LEDs. This lifted degeneracy of polarisation states associated with the ordered GalnP phase has to be considered as a very promising feature for polarisation control in VCSELs.

We report on polarization effects in surface emitting light emitting diodes based on p-i-n AlGaInP/GaInP double heterostructures grown by metal organic vapor phase epitaxy. Devices with an ordered GaInP active layer show polarized light output with a ratio of 4:3 for polarization along the [011] and [011̄] crystal direction, respectively. This polarization is nearly independent of diode current and mesa geometry, but is not observed if disordered GaInP active layers are used. The effect is considered to be an important means for polarization control in vertical cavity surface emitting lasers.

Summary form only given GaInP-AlGaInP is a very promising material for optoelectronic components for the visible spectral range down to 630 nm. Depending on the growth parameter MOVPE-grown AlGaInP alloys (lattice matched to GaAs substrate) show a self ordering in form of a GaP-InP superlattice along the [111] directions. This implies significant changes of the band structure and the optical and electrical properties. We have studied the polarization dependence of the electroabsorption (Franz-Keldysh effect) in AlGaInP-GaInP p-i-n double-hetero structures.

We report on reverse biased photoconductive detectors with novel design and improved high-frequency performance. Taking advantage of the ‘‘giant ambipolar diffusion constant’’ which has been observed previously in n-i-p-i doping superlattices very fast carrier transfer from the inner absorption area to the outer detection area is achieved. The combination of narrow contact spacings and small RC and diffusion time constants results in very high gain-bandwidth products (≳20 GHz) with adjustable 3 dB frequencies.

We report on experimental results on the dynamical behaviour of n-i-p-i based smart pixels, composed of photoconductive switches and electroabsorptive n-i-p-i modulators. For the photoconductive switch we present switching times of 1.9 ns at an optical power of 880 mu W, corresponding to a switching energy of 1.7 pJ. The contrast of the electronic output signal is larger than 10(7) and a maximum dc gain exceeding 10(6) is achieved. For the opto-optical switching contrast ratios of 4:1 at 1.6 mW output power are shown with switching energies of 2.4 fJ/mu m(2) (1.7 pJ). The opto-optical gain is tunable from 10-10(6).

We report on recent theoretical and experimental results on n-i-p-i based smart pixels. We present first results on dynamical switching in these devices. In particular, we present 1.9 ns switching times at an optical power of 880 (mu) W for the photoconductive switch. This corresponds to a total switching energy of 1.7 pJ or 2.4 fJ/micrometers 2 relative to the device area. A contrast of the electronic output signal larger than 107 and a maximum dc gain exceeding 106 is achieved. For an optical NOR gate -- composed of a photoconductive switch and an electroabsorptive n-i-p-i modulator -- we were able to demonstrate operation at optical switching energies of 2 pJ and switching times of 1 microsecond(s) . This corresponds to an opto-optical gain (fan out) of 750. The switching contrast of the optical output signal is 4.5:1.

We report on theoretical and experimental results on a novel metal-semiconductor-metal (MSM) photodetector with a backgate provided by a p-doped layer. The backgate allows extremely short sweep-out times for the holes, due to strong electric fields normal to the surface. Thus, long tails due to slow moving holes and screening of the external drift fields by hole space charge accumulation at high optical power, which lead to a degradation of the time response of conventional MSM photodetectors, are avoided. The high frequency performance measured up to 8 GHz in the time and frequency domain showed a significant reduction of the bandwidth limiting hole tail compared to standard MSM photodetectors.