James Cleary Mcgroddy

GUNN EFFECT IN n‐TYPE InSb

In this letter we report the observation of the Gunn effect in n‐type InSb at 77°K and atmospheric pressure. This result is surprising, since it was previously thought that the large amount of carrier multiplication at fields below the Gunn threshold would preclude observation of the Gunn effect in InSb and similar materials. Several explanations for the negative differential conductivity underlying the Gunn effect in this case are possible, but the intervalley transfer mechanism is most consistent with the observed negative pressure coefficient of the threshold field.

BULK NEGATIVE DIFFERENTIAL CONDUCTIVITY AND TRAVELING DOMAINS IN n‐TYPE GERMANIUM

Measurements have been made on n‐type Ge at 77°K and 27°K, which show the existence of a bulk negative differential conductivity at electric fields above about 3 kV cm−1. This effect is believed to be the cause of previously observed current oscillations, and of traveling domains of high electric field which we have now observed at 27°K.

The gunn effect and conduction band structure in GaxIn1−xSb alloys

Abstract The observation of the Gunn effect in GaxIn1−xSb alloys is reported and shown to be consistent with a conduction band structure having a next higher set of minima along the directions in k space above the lowest conduction band minimum at the center of the Brillouin zone for all values of x.

Electron-hole pair production and gunn effect in InSb☆

Abstract A study of the low and high field transport properties, the Gunn effect and avalanche breakdown as a function of pressure in n-InSb has been used to obtain information about the properties of higher conduction band minima and impurity levels associated with them.

Accurate measurement of the work function of electron-hole drops in germanium

Abstract The work function of electron-hole drops in Ge relative to free excitons is measured by an extremely simple and accurate technique. The threshold excitation power for drop condensation is determined as a function of temperature by observation of the sharp increase in shot noise associated with the drops in a collector junction. The resulting value of the work function is φ = 17.2 ± 1.0 K.

Saturation and recovery of the direct interband absorption in semiconductors

We report observation of dynamical saturation of the optical absorption in direct band−gap semiconductors using mode−locked pulses from a Nd: glass laser. The alloys were of the types InAsxP1−x and Ga1−yInyAs, with x or y chosen so that the direct band gap at room temperature was about 10 meV less than the laser photon energy. Increases in the transmission coefficient of epitaxial thin films by more than 4 orders of magnitude above the equilibrium value have been observed. Using a probe pulse with variable delay with respect to the strong bleaching pulse, we have studied the time dependence of the recovery of the absorption following bleaching and find it to be as short as 30 psec. Thus such alloys may be useful as saturable absorbers for mode locking visible and infrared lasers.

Current oscillations and negative differential conductivity in n-type germanium

The existence of several types of high-frequency majority carrier current instabilities in [100] and [110] oriented samples of n-type germanium has led to a renewed interest in the conductivity of germanium in a strong electric field. We review the experimental situation with regard to these instabilities and show how their properties can be understood in terms of bulk negative differential conductivity, which has been shown to occur in this material for temperatures below about 120°K. The present state of understanding of the origin of this BNDC effect in terms of the band structure and scattering mechanisms in germanium is summarized.

Electron-hole drops in silicon

Abstract Direct experimental evidence for the existence of electron—hole drops in Si has been obtained from the current pulses produced when they dissociate in the high electric field of a p - n junction. From these results we also determine the drop radius, which is typically about 0.75 μ in this experiment.

Interaction between free carriers, free excitons, and electron-hole drops in germanium

Abstract Under steady-state conditions, we have observed an increase of photo-conductivity in Ge at low temperature simultaneously with radiation from electron-hole drops. A set of rate equations for a 3-phase system of carriers, free excitons and drops are used to interpret the results. Values of the exciton-recombination coefficient and the lifetimes of the three phases are determined.

EFFECT OF COMPRESSIVE UNIAXIAL STRESS ON HIGH FIELD DOMAINS IN n‐TYPE Ge

The effect of compressive uniaxial stress on the threshold field for nucleation of high field domains in n‐type Ge at 27°K has been measured. The increase in threshold field is approximately quadratic in stress and is about 15% for a stress of 104 kg/cm2 applied along a 〈100〉 direction parallel to the current and about 37% for a stress of 104 kg/cm2 applied along a 〈100〉 perpendicular to the current. These results indicate that, while in a strong electric field the 〈110〉 valleys are occupied at high stresses, transfer of electrons to these valleys is not the cause of bulk negative differential conductivity in n‐type Ge.