Thermal profiles within the channel of planar gunn diodes using micro-particle sensors

The paper describes the use of a novel microparticle sensor (~3 μm diameter) and infra-red (IR) microscopy to measure the temperature profile within the active channel (typically 3 μm length and 120 μm width) of planar Gunn diodes. The method has enabled detailed temperature measurements showing an asymmetrical temperature profile along the active width of these devices. The asymmetrical temperature profile suggests a similar behaviour in the channel current density, which may contribute to the lower than expected RF output power

Investigation of High-Frequency Fine Structure in the Current Output of Shaped Contact Planar Gunn Diodes

Peer reviewedPostprin

Impact ionisation electroluminescence in planar GaAs-based heterostructure Gunn diodes:Spatial distribution and impact of doping nonuniformities

When biased in the negative differential resistance regime, electroluminescence (EL) is emitted from planar GaAs heterostructure Gunn diodes. This EL is due to the recombination of electrons in the device channel with holes that are generated by impact ionisation when the Gunn domains reach the anode edge. The EL forms non-uniform patterns whose intensity shows short-range intensity variations in the direction parallel to the contacts and decreases along the device channel towards the cathode. This paper employs Monte Carlo models, in conjunction with the experimental data, to analyse these non-uniform EL patterns and to study the carrier dynamics responsible for them. It is found that the short-range lateral (i.e., parallel to the device contacts) EL patterns are probably due to non-uniformities in the doping of the anode contact, illustrating the usefulness of EL analysis on the detection of such inhomogeneities. The overall decreasing EL intensity towards the anode is also discussed in terms of the interaction of holes with the time-dependent electric field due to the transit of the Gunn domains. Due to their lower relative mobility and the low electric field outside of the Gunn domain, freshly generated holes remain close to the anode until the arrival of a new domain accelerates them towards the cathode. When the average over the transit of several Gunn domains is considered, this results in a higher hole density, and hence a higher EL intensity, next to the anode

Investigation of high-frequency fine structure in the current output of shaped contact planar gunn diodes

A novel gallium arsenide (GaAs) planar Gunn diode design with shaped anode and cathode contacts using Monte Carlo simulations has been shown to produce significantly higher frequency fine structure components in the output waveform than the natural transit time frequency of the diode. We have investigated devices without a feed- back potential and devices with a feedback potential (in the delayed mode) and have shown 350-GHz fine structure frequency components in a device with a nominal transit time frequency of 70 GHz is possible. This is the first observation of such stable repeating high-frequency components in a Gunn diode, giving potential for very high-frequency power generation and other wave-shaping applications

10-Year Outcomes after Monitoring, Surgery, or Radiotherapy for Localized Prostate Cancer

BACKGROUND The comparative effectiveness of treatments for prostate cancer that is detected by prostatespecific antigen (PSA) testing remains uncertain. METHODS We compared active monitoring, radical prostatectomy, and external-beam radiotherapy for the treatment of clinically localized prostate cancer. Between 1999 and 2009, a total of 82,429 men 50 to 69 years of age received a PSA test; 2664 received a diagnosis of localized prostate cancer, and 1643 agreed to undergo randomization to active monitoring (545 men), surgery (553), or radiotherapy (545). The primary outcome was prostate-cancer mortality at a median of 10 years of follow-up. Secondary outcomes included the rates of disease progression, metastases, and all-cause deaths. RESULTS There were 17 prostate-cancer-specific deaths overall: 8 in the active-monitoring group (1.5 deaths per 1000 person-years; 95% confidence interval [CI], 0.7 to 3.0), 5 in the surgery group (0.9 per 1000 person-years; 95% CI, 0.4 to 2.2), and 4 in the radiotherapy group (0.7 per 1000 person-years; 95% CI, 0.3 to 2.0); the difference among the groups was not significant (P = 0.48 for the overall comparison). In addition, no significant difference was seen among the groups in the number of deaths from any cause (169 deaths overall; P = 0.87 for the comparison among the three groups). Metastases developed in more men in the active-monitoring group (33 men; 6.3 events per 1000 person-years; 95% CI, 4.5 to 8.8) than in the surgery group (13 men; 2.4 per 1000 person-years; 95% CI, 1.4 to 4.2) or the radiotherapy group (16 men; 3.0 per 1000 person-years; 95% CI, 1.9 to 4.9) (P = 0.004 for the overall comparison). Higher rates of disease progression were seen in the active-monitoring group (112 men; 22.9 events per 1000 person-years; 95% CI, 19.0 to 27.5) than in the surgery group (46 men; 8.9 events per 1000 person-years; 95% CI, 6.7 to 11.9) or the radiotherapy group (46 men; 9.0 events per 1000 person-years; 95% CI, 6.7 to 12.0) (P<0.001 for the overall comparison). CONCLUSIONS At a median of 10 years, prostate-cancer-specific mortality was low irrespective of the treatment assigned, with no significant difference among treatments. Surgery and radiotherapy were associated with lower incidences of disease progression and metastases than was active monitoring. (Funded by the National Institute for Health Research; ProtecT Current Controlled Trials number, ISRCTN20141297; ClinicalTrials.gov number, NCT02044172.) a bs tr ac

Micro-coolers fabricated as a component in an integrated circuit

The packing density and power capacity of integrated electronics is increasing resulting in higher thermal flux densities. Improved thermal management techniques are required and one approach is to include thermoelectric coolers as part of the integrated circuit. An analysis will be described showing that the supporting substrate will have a large influence on the cooling capacity of the thermoelectric cooler. In particular, for materials with a low ZT figure of merit (for example gallium arsenide (GaAs) based compounds) the substrate will have to be substantially thinned to obtain cooling, which may preclude the use of thermoelectric coolers, for example, as part of a GaAs based integrated circuit. Further, using experimental techniques to measure only the small positive cooling temperature difference (ΔT) between the anode (Th) and the cathode (Tc) contacts can be misinterpreted as cooling when in fact it is heating