R.J. Anderson

Excess tunnel currents in AlGaAs/GaAs multiple quantum well infrared detectors

We present experimental evidence of excess tunnel current at low temperatures in AlGaAs/GaAs multiple quantum well infrared detectors that is not accounted for by existing theory. Prior discussions of current mechanisms in these detectors only take into account ideal device properties. For quantum well detectors with thick barrier layers, which are useful for infrared detection, the excess tunnel current component possesses the features of sequential resonant tunneling, i.e., temperature independence of the current, and saturation of the current at intermediate bias voltages with negative conductance oscillations. However, the current is orders of magnitude larger than theory predicts. Comparison with data reported by other groups shows the magnitude of the discrepancy is sample dependent. These results suggest that defects play an important role in determining the tunnel current magnitude. This current component is significant because it limits attainable detector performance at low temperatures for appl...

Effect of heterojunction spike on the quantum efficiency of an AlGaAs/GaAs heterojunction charge coupled device

The ’’spike’’ in the conduction resulting from the band‐gap discontinuity in a p‐ GaAs/n‐Al0.3Ga0.7As heterojunction is observed via the blocking of photoexcited electron flow from the p‐GaAs to the n‐Al0.3Ga0.7As. The spike height deduced from photocurrent versus bias results is 0.14 eV above the conduction‐band minimum of p‐GaAs. This value is 0.13 eV lower than that predicted by theory and suggests a positive interface charge density of 4×1011 cm−2. The lowered barrier does not appear to reduce the electron collection in the charge coupled device operation under low light level illumination.

Microwave performance of GaAs/(Ga,Al)As heterojunction bipolar transistors

. Low frequency noise (in the l/f regime) has been measured for these devices. Equivalent l/f noise input currents on the order of ~ x ~ O ~ O A/ f i z at 100 HZ have been obtained at Ic=lmA, corresponding to extrapolated noise corner frequencies below 1MHz. This result is better than has typically been obtained with GaAs FETs, and indicates that HBTs may be worthwhile in low phase-noise oscillators.

Reduced Geometry GaAs CCD for High Speed Signal Processing

A Schottky barrier gate GaAs CCD is described with high transfer efficiency (>0.999/transfer) and ultra-high speed (fcl.~500 MHz) operation. Predictions for maximum achievable clock frequency are made, and possible signal processing applications are discussed.

A backside‐illuminated imaging AlGaAs/GaAs charge‐coupled device

A glass‐supported, backside‐illuminated AlGaAs/GaAs heterojunction charge‐coupled device (CCD) imager is reported. The CCD structure was grown by liquid phase epitaxy on a GaAs substrate. The top epi‐layer was bonded to glass and the GaAs substrate completely removed. A ten‐pixel three‐phase Schottky gate CCD was fabricated on the glass‐supported layer. The CCD was successfully operated as a line imager with the photosignal entering through the support glass.

GaAlAs/GaAs heterojunction Schottky barrier gate CCD

A buried channel Schottky barrier gate GaAlAs/GaAs CCD is described. Device structures, fabrication techniques and results are discussed. Charge transfer efficiency of 0.9993 per transfer has been measured on these 30 gate (10 pixel) CCDs. Dark current was found to be about an order of magnitude lower in GaAlAs than in GaAs. The best Ga.78Al.22As device has between 2 to 4nA/cm2at room temperature.

Low dark current glass bonded AlGaAs/GaAs Schottky gate imaging CCD

The fabrication and characterization of a glass bonded, backside illuminated, AlGaAs/GaAs heterojunction CCD imager is reported. The dark current of these devices is found to be <1 nA/(cm²which indicates that the glass bonding procedure does not adversely effect the dark current device performance. To isolate process induced degradation of the CCD Schottky gates, diodes were fabricated on n-Al<inf>x</inf>Ga<inf>1-x</inf>As (0 ≤ × ≤ 0.55) by e-beam evaporation of Cr/AuGe, Ti/Pt/Au and Cr/Au. The data indicate that φ<inf>Bn</inf>(Cr) ≤ φ<inf>Bn</inf>(Ti) for all solid compositions examined. Low temperature annealing causes a degradation of the Cr/AuGe and Ti/Pt/Au devices; however, the characteristics of the Cr/Au diodes improve significantly

An ultra high speed GaAs CCD

An ultra high speed buried channel Schottky barrier gate GaAs CCD is described which has been operated up to a clock frequency of 500 MHz. The transit time limited upper clock frequency is predicted to exceed 5 GHz.

Effect of proton bombardment isolation on the DC and transient characteristics of Schottky barriers on Al x Ga 1-x As

The dark current of Schottky barrier diodes on n-AlGaAs/p-GaAs/n+GaAs structures isolated with a proton bombardment guard ring is measured as a function of proton dose. It was found that the optimum proton dose is near 1014cm-2which resulted in a dark current of 130 pA/cm2. The DC leakage currents are much greater than the dark currents under charge integration conditions and can be explained as a hole current from the p-GaAs to the Schottky metal.

High speed GaAs CCD

A GaAs CCD with high transfer efficiency is described and implications for high speed devices fabricated with this technology are described.