The high electron mobility transistor's (HEMT's) noise behavior is presented from theoretical and experimental points of view. The general method used in the high-frequency noise analysis is described and the different approximations commonly used in the derivation of the noise parameter expressions are discussed. A comparison between the noise performance of both MESFETs and HEMTs is carried out. The measurement techniques providing the noise figure and the other noise parameters are then described and compared. >

Noise modeling and measurement techniques (HEMTs)

The low-frequency noise characteristics of N-p-n Al/sub x/Ga/sub 1-x/As/GaAs heterojunction bipolar transistors (HBTs) have been investigated as a function of bias current, device geometry, extrinsic-base-surface condition, Al mole fraction in the emitter, and temperature in order to identify the dominant noise mechanisms. These measurements show the existence of three distinct regions in the noise spectra: a 1/f noise line shape, a Lorentzian spectrum (noise 'bump'), and a white-noise region. The 1/f noise is attributed to fluctuations in the extrinsic-base surface recombination current. The noise bump is generated by an AlGaAs trap in the emitter-base junction. The DX center was identified as a possible candidate for this trap. It is shown that for 4- mu m*10- mu m emitter AlGaAs/GaAs HBTs, the use of a depleted, AlGaAs passivation ledge over the extrinsic-base surface typically reduced the 1/f base noise current by a factor of 10, and the reduction of the Al mole fraction from 0.3 to 0.2 decreased the magnitude of the noise bump by a factor of 3. >

Low-frequency noise properties of N-p-n AlGaAs/GaAs heterojunction bipolar transistors

We have measured the generation‐recombination noise from the donor‐related DX centers in current biased GaAs/AlxGa1−xAs heterostructures from 1 Hz to 25 kHz and from 77 to 330 K. A significant noise contribution from these traps is observed even at Al mole fractions below 0.2, where the trap level is resonant with the conduction band. The activated behavior of the noise spectrum from this resonant level is very similar to that observed at higher Al mole fractions, when the level lies deep in the fundamental gap. This result can be predicted, based on the recently elucidated relationship of the trap level to the band structure of AlxGa1−xAs. In accordance with other experimental results, the noise spectra demonstrate that the emission and capture kinetics of the level are unperturbed by its resonance with the conduction band. We briefly discuss some implications of these results for heterostructure transistor design.

Noise spectroscopy of deep level (DX) centers in GaAs‐AlxGa1−xAs heterostructures

The presence of traps in GaInP/GaAs and AlGaAs/GaAs HEMT's was investigated by means of low frequency noise and frequency dispersion measurements. Low frequency noise measurements showed two deep traps (E/sub a1/=0.58 eV, E/sub a2/=0.27 eV) in AlGaAs/GaAs HEMT's. One of them (E/sub a2/) is responsible for the channel current collapse at low temperature. A deep trap (E/sub a1/'=0.52 eV) was observed in GaInP/GaAs HEMT's only at a much higher temperature (/spl sim/350 K). These devices showed a transconductance dispersion of /spl sim/16% at 300 K which reduced to only /spl sim/2% at 200 K. The dispersion characteristics of AlGaAs/GaAs HEMT's were very similar at 300 K (/spl sim/12%) but degraded at 200 K (/spl sim/20%). The low frequency noise and the transconductance dispersion are enhanced at certain temperatures corresponding to trap level crossing by the Fermi-level. The transition frequency of 1/f noise is estimated at 180 MHz for GaInP/GaAs HEMT's and resembles that of AlGaAs/GaAs devices. >

Trap studies in GaInP/GaAs and AlGaAs/GaAs HEMT's by means of low-frequency noise and transconductance dispersion characterizations

Low-frequency noise measurements were performed on n-GaAs/undoped AlAs superlattice MODFET structures in the temperature and frequency ranges from 50 to 270 K and 1 Hz to 25 kHz, respectively. In both the ohmic and the velocity-saturated regime, generation-recombination (g-r) noise was dominant. Two electron traps were detected. The structure of the noise spectra in the velocity-saturated and ohmic regime were similar, but were smaller by several orders of magnitude in the latter case. For temperatures above 250 K the measurements show an additional 1/f noise at low frequencies in the velocity-saturation regime. A model that explains the g-r noise in the velocity-saturated part of the channel is proposed and applied successfully to the experimental data. >

Generation-recombination noise in the saturation regime of MODFET structures

Low-frequency noise of (AlGa)As-GaAs heterostructures grown by molecular-beam epitaxy was investigated. The temperature of the samples was varied between 100 and 400 K. In the frequency range from 1 Hz to 25 kHz noise spectra can be described as superposition of several generation-recombination (GR) noise components. Four deep levels (E = 0.40, 0.42, 0.54, 0.60 eV) were detected, three of which are in agreement with those measured independently by deep-level transient spectroscopy (DLTS).

K. Heime

Papers

Deep-level analysis in (AlGa)As—GaAs 2-D electron gas devices by means of low-frequency noise measurements

K. Heime

Papers

Deep-level analysis in (AlGa)As&#8212;GaAs 2-D electron gas devices by means of low-frequency noise measurements

Deep-level analysis in (AlGa)As—GaAs 2-D electron gas devices by means of low-frequency noise measurements