Misfit stress in InGaAs/InP heteroepitaxial structures grown by hydride‐transport vapor phase epitaxy has been studied using an x‐ray technique to measure the wafer curvature and using an x‐ray double crystal diffractometer to measure mismatches. The stress calculated from the measured radius of curvature was, in all cases, found to be smaller than the value predicted from the lattice mismatch using the simple beam theory and assuming a coherent interface. A simple argument is used to show that the parallel mismatch is directly related to the density of misfit dislocations. By taking into account both the presence of misfit dislocations and tetragonal distortion, relationships between the curvature, density of interfacial misfit dislocations, relaxed lattice mismatch, and measured tetragonally distorted vertical and parallel mismatches are derived. Predicted values for the radius of curvature agree very well with measured values. The results also indicate that in the presence of interfacial misfit disloca...

Misfit stress in InGaAs/InP heteroepitaxial structures grown by vapor‐phase epitaxy

We have measured the magnitude of the conduction‐band discontinuities at heterojunctions for several compositions of InGaAsP grown lattice matched on InP. We find that the conduction‐band discontinuity (ΔEc) is related to the difference in band gaps (ΔEg) between the InGaAsP and InP layers via ΔEc =0.39(ΔEg). Thus, 40% of the band‐gap difference lies in the conduction band of this material system. The measurements were made on a series of composition of InGaAsP spanning the alloy range from In0.53Ga0.47As (with energy gap Eg =0.75 eV) to InP (Eg =1.35 eV) using capacitance‐voltage techniques. Depletion deep into the semiconductor layers was facilitated by the formation of organic‐on‐inorganic semiconductor contact barriers on the InGaAsP surface.

Relationship between the conduction‐band discontinuities and band‐gap differences of InGaAsP/InP heterojunctions

A simplified algorithm for calculating time response of avalanche photodiodes (APDs) is presented. The algorithm considers the time course of avalanche processes for the general case of position-dependent double-carrier multiplications including the dead space effect. The algorithm is based on a discrete time setting ideally suited for computer modeling and can be applied to any APD structure. It gives a fast and accurate estimation of the time and frequency response of APDs. As an example, the present method is applied to InP-InGaAs separate absorption, grading, charge, and multiplication (SAGCM) APDs. The variation of multiplication pain with bias voltage and 3-dB electrical bandwidth at different multiplication gain obtained using the new algorithm show good agreement with experimental results. The algorithm can be used to study temperature dependence of APD characteristics and can be easily extended to calculate the excess noise factor.

A simplified approach to time-domain modeling of avalanche photodiodes

In this paper, we investigate temperature dependence of breakdown voltage V/sub br/ from -40 to 110/spl deg/C in separate absorption, grading, charge, and multiplication (SAGCM) InP/InGaAs avalanche photodiodes (APD's) with a range of device parameters. The experimental data shows that V/sub br/ is approximately a linear function of temperature, with a temperature coefficient /spl eta//sub exp/ between 0.13 and 0.16 V//spl deg/C. A physical model is developed and it demonstrates that V/sub br/ indeed varies linearly with temperature with a temperature coefficient /spl eta//sub the/ about 0.155 V//spl deg/C. It also explains successfully the small variation of /spl eta//sub exp/ among the APD's. Good agreement between the physical model predictions and experimental data of published InP-based APD's is also obtained. This good agreement demonstrates that the proposed physical model is appropriate to model the temperature dependent characteristics in any InP-based APD's. >

Temperature dependence of breakdown voltages in separate absorption, grading, charge, and multiplication InP/InGaAs avalanche photodiodes

A new variably spaced superlattice energy filter is proposed which provides high‐energy injection of electrons into a bulk semiconductor layer based on resonant tunneling between adjacent quantum well levels which are brought into alignment by an applied bias. Applications of this concept to a variety of optoelectronic devices and to thin‐film electroluminescent devices and photodetectors are discussed.

Variably spaced superlattice energy filter, a new device design concept for high-energy electron injection

The doping profiles, current-voltage (I–V) and photoresponse characteristics of five In0.53Ga0.47As/InP avalanche photodiode (APD) wafers are presented. A detailed analysis indicates that the dark current is due largely to generation and recombination of carriers in the diode bulk, and in some wafers tunneling at the p-n junction is dominant near breakdown (VB). In some cases, significant surface currents are also observed. In three high-performance wafers, however, low primary dark currents (∼5 nA) with no evidence for tunnelling at 0.99 VB have been obtained. In addition, microplasmas have been found in some wafers, due to local breakdown possibly arising from crystalline defects. Nevertheless, we report uniform gains as high as 100. The dark current and gain characteristics of these devices are among the best reported to date for In0.53Ga0.47As/InP APDs. Finally, the response of the APDs to fast optical pulses has been analyzed at both low and high illumination intensity. The slow speed of response, which has been reported elsewhere, is considered in detail and is found to be due to charge pile-up at the abrupt n-In0.53Ga0.47As/n-InP heterointerface which is characteristic of our devices. Using an analysis of the response time thermal activation energy along with the transient pulse shape, we infer that the heterointerfaces are graded over a length of 2 L ≌ 300 A . The model predicts that fast response can be obtained for heterointerface grading lengths of 2 L ⩾ 500 A , depending on the epitaxial layer doping and extent of penetration of the depletion region into the In0.53Ga0.47As layer at breakdown.

S.R. Forrest

Papers

Analysis of the dark current and photoresponse of In0.53Ga0.47As/InP avalanche photodiodes